20646 Federal Register /Vol. 61, No. 89/Tuesday, May 7

20646 Federal Register / Vol. 61, No. 89 / Tuesday, May 7, 1996 / Rules and Regulations

‘‘WARNINGSevere icing may result from

environmental conditions outside of those forwhich the airplane is certificated. Flight infreezing rain, freezing drizzle, or mixed icingconditions (supercooled liquid water and icecrystals) may result in ice build-up onprotected surfaces exceeding the capability ofthe ice protection system, or may result in iceforming aft of the protected surfaces. This icemay not be shed using the ice protectionsystems, and may seriously degrade theperformance and controllability of theairplane.

• During flight, severe icing conditionsthat exceed those for which the airplane iscertificated shall be determined by thefollowing visual cues. If one or more of thesevisual cues exists, immediately requestpriority handling from Air Traffic Control tofacilitate a route or an altitude change to exitthe icing conditions.—Unusually extensive ice accreted on the

airframe in areas not normally observed tocollect ice.

—Accumulation of ice on the lower surfaceof the wing aft of the protected area.

—Accumulation of ice on the propellerspinner farther aft than normally observed.• Since the autopilot may mask tactile

cues that indicate adverse changes inhandling characteristics, use of the autopilotis prohibited when any of the visual cuesspecified above exist, or when unusuallateral trim requirements or autopilot trimwarnings are encountered while the airplaneis in icing conditions.

• All icing detection lights must beoperative prior to flight into icing conditionsat night. [NOTE: This supersedes any reliefprovided by the Master Minimum EquipmentList (MMEL).]’’

(2) Revise the FAA-approved AFM byincorporating the following into theProcedures Section of the AFM. This may beaccomplished by inserting a copy of this ADin the AFM.

‘‘THE FOLLOWING WEATHERCONDITIONS MAY BE CONDUCIVE TOSEVERE IN-FLIGHT ICING:

• Visible rain at temperatures below 0degrees Celsius ambient air temperature.

• Droplets that splash or splatter on impactat temperatures below 0 degrees Celsiusambient air temperature.

PROCEDURES FOR EXITING THE SEVEREICING ENVIRONMENT:

These procedures are applicable to allflight phases from takeoff to landing. Monitorthe ambient air temperature. While severeicing may form at temperatures as cold as¥18 degrees Celsius, increased vigilance iswarranted at temperatures around freezingwith visible moisture present. If the visualcues specified in the Limitations Section ofthe AFM for identifying severe icingconditions are observed, accomplish thefollowing:

• Immediately request priority handlingfrom Air Traffic Control to facilitate a routeor an altitude change to exit the severe icingconditions in order to avoid extendedexposure to flight conditions more severethan those for which the airplane has beencertificated.

• Avoid abrupt and excessivemaneuvering that may exacerbate controldifficulties.

• Do not engage the autopilot.• If the autopilot is engaged, hold the

control wheel firmly and disengage theautopilot.

• If an unusual roll response oruncommanded roll control movement isobserved, reduce the angle-of-attack.

• Do not extend flaps during extendedoperation in icing conditions. Operation withflaps extended can result in a reduced wingangle-of-attack, with the possibility of iceforming on the upper surface further aft onthe wing than normal, possibly aft of theprotected area.

• If the flaps are extended, do not retractthem until the airframe is clear of ice.

• Report these weather conditions to AirTraffic Control.’’

(b) Incorporating the AFM revisions, asrequired by this AD, may be performed bythe owner/operator holding at least a privatepilot certificate as authorized by section 43.7of the Federal Aviation Regulations (14 CFR43.7), and must be entered into the aircraftrecords showing compliance with this AD inaccordance with section 43.11 of the FederalAviation Regulations (14 CFR 43.11).

(c) Special flight permits may be issued inaccordance with sections 21.197 and 21.199of the Federal Aviation Regulations (14 CFR21.197 and 21.199) to operate the airplane toa location where the requirements of this ADcan be accomplished.

(d) An alternative method of compliance oradjustment of the compliance time thatprovides an acceptable level of safety may beused if approved by the Manager, SmallAirplane Directorate, FAA, 1201 Walnut,suite 900, Kansas City, Missouri 64106. Therequest shall be forwarded through anappropriate FAA Maintenance Inspector,who may add comments and then send it tothe Manager, Small Airplane Directorate.

Note 3: Information concerning theexistence of approved alternative methods ofcompliance with this AD, if any, may beobtained from the Small AirplaneDirectorate.

(e) All persons affected by this directivemay examine information related to this ADat the FAA, Central Region, Office of theAssistant Chief Counsel, Room 1558, 601 E.12th Street, Kansas City, Missouri 64106.

(f) This amendment (39–9593) becomeseffective on June 11, 1996.

Issued in Kansas City, Missouri, on April24, 1996.Henry A. Armstrong,Acting Manager, Small Airplane Directorate,Aircraft Certification Service.[FR Doc. 96–10727 Filed 5–1–96; 3:25 pm]BILLING CODE 4910–13–P

14 CFR Part 39

[Docket No. 95–NM–146–AD; Amendment39–9604; AD 96–09–28]

RIN 2120–AA64

Airworthiness Directives; AerospatialeModel ATR–42 and ATR–72 SeriesAirplanes

AGENCY: Federal AviationAdministration, DOT.ACTION: Final rule.

SUMMARY: This amendment supersedesan existing airworthiness directive (AD),applicable to all Aerospatiale ModelATR–42 and ATR–72 series airplanes.Unless modifications are accomplishedor alternative procedures and trainingare adopted, that AD currently prohibitsoperation of the airplane in certain icingconditions, and requires restrictions onthe use of the autopilot in certainconditions. That AD was prompted byan FAA determination that, duringflight, in certain icing conditions, andwith the airplane in a specific flightconfiguration, a ridge of ice can form onthe wing and cause an interruption inthe airflow over the ailerons, ailerondeflection, and resultant lateral controlforces. The actions specified by that ADare intended to prevent a roll upset fromwhich the flight crew may be unable torecover. This action adds requirementsfor modification of the deicing boots onthe leading edge of the wing and variousfollow-on actions. This action alsoremoves certain limitations andprocedures.DATES: Effective June 11, 1996.

The incorporation by reference ofcertain publications, as listed in theregulations, is approved by the Directorof the Federal Register as of June 11,1996.

The incorporation by reference ofAerospatiale Service Bulletin ATR72–27–1039, dated January 12, 1995, listedin the regulations was approvedpreviously by the Director of the FederalRegister as of March 8, 1995 (60 FR9616, February 21, 1995).ADDRESSES: The service informationreferenced in this AD may be obtainedfrom Aerospatiale, 316 Route deBayonne, 31060 Toulouse, Cedex 03,France. This information may beexamined at the Federal AviationAdministration (FAA), TransportAirplane Directorate, Rules Docket,1601 Lind Avenue, SW., Renton,Washington; or at the Office of theFederal Register, 800 North CapitolStreet, NW., suite 700, Washington, DC.FOR FURTHER INFORMATION CONTACT: GaryLium, Aerospace Engineer,Standardization Branch, ANM–113,

20647Federal Register / Vol. 61, No. 89 / Tuesday, May 7, 1996 / Rules and Regulations

FAA, Transport Airplane Directorate,1601 Lind Avenue, SW., Renton,Washington 98055–4056; telephone(206) 227–1112; fax (206) 227–1149.SUPPLEMENTARY INFORMATION: Aproposal to amend part 39 of the FederalAviation Regulations (14 CFR part 39)by superseding AD 95–02–51,amendment 39–9152 (60 FR 9616,February 21, 1995), which is applicableto all Aerospatiale Model ATR–42 andATR–72 series airplanes, was publishedas a supplemental notice of proposedrulemaking (NPRM) in the FederalRegister on January 25, 1996 (61 FR2147). The action proposed to prohibit

operation of the airplane in certain icingconditions unless modifications areaccomplished or alternatives proceduresand training are adopted, and to requirerestrictions on the use of the autopilotin certain conditions. The action alsoproposed to add requirements formodification of the deicing boots on theleading edge of the wing and variousfollow-on actions. In addition, theaction proposed to remove certainlimitations and procedures.

Disposition of Comments

Interested persons have been affordedan opportunity to participate in the

making of this amendment. Dueconsideration has been given to thecomments received.

In addition to the proposed ruledescribed previously, in January 1996,the FAA issued 17 other similarproposals that address the subjectunsafe condition on various airplanemodels (see below for a listing of all 18proposed rules). These 17 proposals alsowere published in the Federal Registeron January 25, 1996. This final rulecontains the FAA’s responses to allpublic comments received for each ofthese proposed rules.

Docket No. Manufacturer/airplane model FEDERAL REGISTERcitation

96–CE–01–AD de Havilland DHC–6 Series .............................................................................................................. 61 FR 217596–CE–02–AD EMBRAER EMB–110P1/EMB–110P2 .............................................................................................. 61 FR 218396–CE–03–AD Beech 99/200/1900 Series ................................................................................................................ 61 FR 218096–CE–04–AD Dornier 228 Series ............................................................................................................................ 61 FR 217296–CE–05–AD Cessna 208/208B .............................................................................................................................. 61 FR 217896–CE–06–AD Fairchild Aircraft SA226/SA227 Series ............................................................................................. 61 FR 218996–CE–07–AD Jetstream 3101/3201 ......................................................................................................................... 61 FR 218696–NM–13–AD Jetstream BAe ATP ........................................................................................................................... 61 FR 214496–NM–14–AD Jetstream 4101 .................................................................................................................................. 61 FR 214296–NM–15–AD British Aerospace HS 748 Series ...................................................................................................... 61 FR 213996–NM–16–AD Saab SF340A/SAAB 340B/SAAB 2000 Series ................................................................................. 61 FR 216996–NM–17–AD CASA C–212/CN–235 Series ............................................................................................................ 61 FR 216696–NM–18–AD Dornier 328–100 Series .................................................................................................................... 61 FR 215796–NM–19–AD EMBRAER EMB–120 Series ............................................................................................................. 61 FR 216396–NM–20–AD de Havilland DHC–7/DHC–8 Series .................................................................................................. 61 FR 215496–NM–21–AD Fokker F27 Mark 100/200/300/400/500/600/700/050 Series ............................................................ 61 FR 216096–NM–22–AD Short Brothers SD3–30/SD3–60/SD3–SHERPA Series ................................................................... 61 FR 215195–NM–146–AD Aerospatiale ATR–42/ATR–72 Series ............................................................................................... 61 FR 2147

Comment 1. Support for the ProposalsNumerous commenters support the

FAA’s intent to minimize the potentialhazards associated with operatingairplanes of any type design in severeicing conditions. One commenter statesthat the limitation prohibiting the use offlaps while enroute and during holdingin icing conditions will be a positivecontribution to safety. Additionally,several commenters support therequirement of the proposed AD forAerospatiale airplanes for installation ofmodified deicing boots on the outerleading edges of the wings. One of thesecommenters states that theincorporation of AFM procedures, inaddition to installation of the modifiedboots, provide a substantial margin ofsafety for the Aerospatiale fleet.

Comment 2. Requests ConcerningReferences to ‘‘Freezing Rain/FreezingDrizzle’’

Raytheon requests that references to aclass of meteorological conditions in thelimitations described as ‘‘freezing rainor freezing drizzle’’ should be removedfrom the proposed rules. Raytheoncontends that instructions for the flight

crew should be restricted to hazardousconditions that are defined by theaccumulation of ice. The commenterstates that the term ‘‘severe icing’’ hasa specific meaning as defined in theAeronautical Information Manual: ‘‘Therate of accumulation is such that theicing/anti-icing equipment fails toreduce or control the hazard. Immediatediversion is necessary.’’ The commenterstates that, although freezing rain orfreezing drizzle may involve dropslarger than those specified in AppendixC of part 25 (‘‘Airworthiness Standards:Transport Category Airplanes’’) of theFederal Aviation Regulations (14 CFRpart 25), flight into those conditionsdoes not always result in accumulationof ice beyond the capability of theaircraft nor is severe icing always theresult of freezing rain or freezingdrizzle. Raytheon concludes that thelimitation specified in paragraph (a)(1)of the proposals which reads, ‘‘Flight inmeteorological conditions described asfreezing rain or freezing drizzle, asdetermined by the following visualcues, is prohibited,’’ is an inference orconclusion that does not follow from thepremises.

The European Regional Airlines(ERA) Association states that theproposals define visual cues to be usedto identify ‘‘freezing rain’’ and ‘‘freezingdrizzle,’’ but these criteria areinconsistent with the criteria defined bythe International Civil AviationOrganization (ICAO) and used byweather observers in aviationmeteorological support services. TheFAA infers from this remark that ERArequests the use of ICAO terminologyassociated with the visual cues.

The FAA concurs partially. The FAAconcurs that most of the references to‘‘freezing rain/freezing drizzle’’ can beremoved from the final rules. The FAAhas revised the final rules to replacecertain references to freezing rain andfreezing drizzle with the words ‘‘severeicing.’’ The FAA finds that since thevisual cues contained in paragraph(a)(1) of these final rules indicate thaticing conditions have exceeded thelimits of the ice protection equipment,the use of the terminology ‘‘severeicing’’ is appropriate. As stated by onecommenter, ‘‘severe icing’’ isterminology used to describe icingconditions that exceed the capabilities


of the ice protection equipment. Theterminology ‘‘severe icing’’ is commonlyused and understood within theaviation community. Additionally, thereshould be no confusion over the use ofthis term in the final rules because theAFM revisions required by these AD’sdefine the terminology ‘‘severe icing’’ byspecifying the visual cues that indicatewhen the capabilities of the iceprotection equipment have beenexceeded. However, the FAA wouldconsider a request for approval of analternative method of compliance to useterminology other than ‘‘severe icing’’ inan AFM, in accordance with theprovisions of these AD’s, provided thatadequate justification is presented tosupport such a request.

Any inconsistencies that may existbetween the criteria used by weatherspecialists to define ‘‘severe icing’’ andthe criteria stated in these final rules arenot relevant for these AD’s becausethese AD’s do not require the flight crewto take any action based on informationprovided by a weather observer. Forthese AD’s, the flight crew must onlytake action if certain visual cues arepresent on the airplane.

The FAA has determined thatreference to freezing rain and freezingdrizzle should not be removed from thetext of the ‘‘Caution’’ that appears inparagraph (a)(2) of the proposals. [Note:The ‘‘Caution’’ appears as the‘‘Warning’’ in paragraph (a)(1) of thefinal rules. An explanation of thischange is contained in the disposition ofComment 49 of these final rules.]Reference to freezing rain and freezingdrizzle in that portion of text is madesimply to provide a description ofconditions that may result in ice build-up that exceeds the capabilities of theice protection system.

Comment 3. Request for Review of‘‘Severe Icing’’ Terminology

One commenter, the Civil AviationAuthority (CAA), which is theairworthiness authority for the UnitedKingdom, requests that use of theterminology ‘‘severe icing’’ be reviewed.The CAA does not believe it isappropriate that this terminologybecomes accepted for supercooled largedroplet (SLD) conditions. The CAAindicates that a common interpretationfor ‘‘severe icing’’ is that beyond thelimit specified in Appendix C of part 25of the Federal Aviation Regulations (14CFR part 25), which is at or just over thecapability of the ice protection system.

The FAA has reviewed the use of theterminology ‘‘severe icing’’ as related toSLD. The FAA finds that ice resultingfrom SLD conditions may not alwaysmeet the criterion specified in the

common interpretation of ‘‘severeicing,’’ as described by the commenter.The FAA notes that while SLDconditions may result in the formationof severe icing, severe icing also mayaccrue in conditions such as liquidwater content, temperature, or extent ofcloud, when those conditions exceedthe limits specified in Appendix C ofpart 25 of the Federal AviationRegulations (14 CFR part 25). Asexplained previously, most references tofreezing rain and freezing drizzle havebeen replaced with the terminology‘‘severe icing.’’ Additionally, the AFM’sfor the affected airplanes include adefinition of severe icing.

Comment 4. Request To Withdraw theProposals: Significant Economic Impacton Operating Community

A number of commenters request thatthe proposals be withdrawn because theeffect of these proposed AD’s willproduce a significant economic impacton the operating community. Thecommenters indicate that many flightswould need to be canceled in order tomake all reasonable efforts to avoidencounters with freezing rain/freezingdrizzle conditions—i.e., when theseconditions are forecast, airplanes will beprohibited from flight into thoseconditions. One commenter remarksthat, based on the actual weather inJanuary 1996, nearly 75 percent of itsscheduled flights would have beencanceled due to forecast or actualfreezing rain or freezing drizzleconditions if the AD’s had been ineffect. The commenters do not believethat the FAA has considered theeconomic factors affected by theproposed actions, such as the number offlights lost per day, crew costs,passenger compensation, misconnectedbaggage, etc.

If the FAA does not withdraw theproposals, one commenter states thatthe prohibition of flight in freezing rainor freezing drizzle, as specified inparagraph (a)(1) of the proposals, shouldbe revised. The commenter suggests thefollowing: ‘‘The aircraft should beimmediately flown clear of icingconditions if ice is seen forming on theupper surface of the wing behind theleading edge deice boots.’’ Thecommenter believes that the currentwording in the proposals would causeflight crews to cancel or delay departurenot only when freezing rain or freezingdrizzle exists, but also when thoseconditions are forecast.

The FAA concurs partially. The FAAfinds that some misunderstanding existsamong the commenters concerning theintent of these AD’s. Many of thecommenters believe that the AD’s will

prevent affected airplanes from flight inforecast freezing rain and freezingdrizzle. This is not the case. The FAAagrees that certain language containedin the AD’s must be clarified to reflectits intent. The FAA has evaluated thewording proposed by one of thecommenters and agrees with it inprincipal. However, the FAA hasdetermined that the first limitation inparagraph (a)(1) of the final rules mustbe revised in order to accommodatevisual cues other than that specified bythe commenter, to incorporateterminology familiar to the flight crew,and to emphasize that these AD’saddress only in-flight icing encounters.Additionally, in order to ensure thatappropriate coordination with AirTraffic Control is accomplished, theFAA has revised the instructionfollowing the visual cues in paragraph(a)(1), and has moved that instruction tothe end of the first limitation inparagraph (a)(1) of the final rules. Theentire limitation reads as follows:‘‘During flight, severe icing conditionsthat exceed those for which the airplaneis certificated shall be determined bythe following visual cues. If one or moreof these visual cues exists, immediatelyrequest priority handling from AirTraffic Control to facilitate a route or analtitude change to exit the icingconditions.’’ (Operators should notethat, in the final rule for Aerospatialeairplanes, only one visual cue isspecified. That cue involves ice on theside window of the airplane.)

Several commenters question certainissues related to dispatch of the airplanein severe icing conditions. Onecommenter states that the proceduresspecified in the proposed AD’s fail toaddress the conditions that wouldprohibit takeoff in freezing rain andfreezing drizzle. The commenterbelieves the visual cues provided in theproposals would only appear on anairplane during flight. Thus, allowableconditions for takeoff during times offorecast freezing rain or freezing drizzleare left to the individual operator’sinterpretation. Another commenterbelieves that the FAA has notestablished a basis for prohibiting flightin all reported freezing drizzle. Thecommenter contends that takeoff infreezing rain should always beprevented, but takeoff in freezing drizzleshould be possible after applyingappropriate deicing or anti-icingtreatments. One commenter requeststhat the FAA clarify how the proceduresfor exiting freezing rain/freezing drizzleconditions would apply to takeoff andlanding. The commenter states thatlanding during those conditions might,


in many cases, be the most expeditiousmethod of avoiding a hazardouscondition. Another commenter suggeststhat the AFM for Aerospatiale airplanesshould be revised to reflect standarddispatch rules; however, the commenterprovides no justification for this request.

The FAA concurs that visual cues thatwould prohibit takeoff in freezing rainor freezing drizzle were not providedbecause the FAA’s intent is that theseAD’s address only in-flight icingencounters. These AD’s do not affectany existing regulations or FAA-approved operating procedures relatedto takeoff, dispatch, or release of anairplane in icing conditions. These AD’sonly prohibit remaining in icingconditions when certain visual cues arepresent on the airplane; these AD’s donot prohibit flight into forecast orreported freezing drizzle. Operatorsmust comply with existing rules thatrequire an airplane to be free of ice priorto takeoff. Further, the FAA finds noneed to revise the AFM for Aerospatialeairplanes to reflect standard dispatchrules. The FAA also considers thatlanding the airplane when freezing rain/freezing drizzle conditions areencountered would, in many cases, bethe most expeditious method of exitingthe conditions. Such landing would bein compliance with the limitation thatrequires the flight crew to exit thesevere icing conditions.

Two commenters indicate that thefirst note that appears in paragraph(a)(1) of the proposed rules could beinterpreted to mean that if freezing rainor freezing drizzle is forecast anywherealong the route of flight, the airplanecould not be dispatched. One of thecommenters concludes that forecastingmethodologies are inadequate andwould need to be improved. The othercommenter suggests that the FAAremove the word ‘‘purely’’ from thenote. The same commenter requests thatthe FAA clarify that the airplane may bedispatched if the forecast may indicatefreezing rain/freezing drizzleconditions. Another commenterindicates that the wording of the samenote is unclear as to how the FAAdefines a ‘‘purely’’ inadvertentencounter. The commenter states thatexamples of such purely inadvertentencounters would be helpful.

One commenter asks the followingquestions in regard to the same note:—What are ‘‘reasonable efforts?’’—What does ‘‘immediately exit’’ mean?

Are the procedures for immediatelyexiting listed in the Air TrafficController’s Handbook or theAirman’s Information Manual? Can apilot operating the airplane in a

holding pattern decide on his/herown to immediately descend belowthe freezing level without regard toother traffic?One commenter states that the note

should be placed in the NormalProcedures Section of the AFM, ratherthan in the Limitations Section. Thecommenter provides no justification forthis request.

The FAA concurs that clarification ofthis note is necessary. The FAAoriginally included the note in the AD’sto clarify the intent of the rules. Sincethe first instruction and the limitationthat follows have been revised in thesefinal rules, the FAA finds that inclusionof the clarifying note is no longernecessary. In order to avoid any possiblemisinterpretation of the intent of thelimitation on flight in freezing rain orfreezing drizzle, the FAA has removedthe first note that appeared in paragraph(a)(1) of the proposals. These AD’s donot prohibit flight into forecast orreported freezing rain or freezingdrizzle. This means that the aircraft isnot prohibited from takeoff, dispatch, orrelease simply because the forecast mayindicate freezing rain or freezing drizzle,but is prohibited from continued flightin severe icing conditions.

Comment 5. Request To Withdraw theProposals: No Unsafe Condition HasBeen Established

Several commenters request that theproposals be withdrawn because nounsafe condition has been establishedwith respect to airplane handlingcharacteristics in severe icingconditions. One commenter states thatthe preamble of the proposals does notprovide data that establish an unsafecondition; the preamble only indicatesthat there are inadequate data torepresent all possible conditions.Another commenter remarks that theFAA’s dismissal of the significance ofthe test results with the speciouscomment, ‘‘such airplanes coulddevelop ice shapes other than thosetested,’’ is wholly speculative, and is aninvalid basis on which to issue an ADunder the provisions of part 39(‘‘Airworthiness Directives’’) of theFederal Aviation Regulations (14 CFRpart 39).

The FAA does not concur that theseAD’s should be withdrawn. As stated inthe preamble to the proposals, the FAAhas not required that airplanes beshown to be capable of operating safelyin icing conditions outside the icingcertification envelope specified inAppendix C of part 25 of the FederalAviation Regulations (14 CFR part 25).This means that any time an airplane isflown in icing conditions for which it is

not certificated, there is a potential foran unsafe condition to exist or developand the flight crew must take steps toexit those conditions expeditiously.Further, the FAA has determined thatflight crews are not currently providedwith adequate information necessary todetermine when an airplane is operatingin icing conditions for which it is notcertificated or what action to take whensuch conditions are encountered. Theabsence of this information presents anunsafe condition because without thatinformation, a pilot may remain in icingconditions for which the airplane hasnot been proven to be safe. These AD’scorrect the unsafe condition byrequiring AFM revisions that providethe flight crews with visual cues todetermine when icing conditions havebeen encountered for which the airplaneis not certificated, and by providingprocedures to safely exit thoseconditions.

Additionally, in the preamble to theproposed rules, the FAA discussed theinvestigation of roll control anomalies toexplain that this investigation was not acomplete certification program. Thetesting was designed to examine onlythe roll handling characteristics of theairplane in certain droplets the size offreezing drizzle. The testing was not acertification test to approve the airplanefor flight into freezing drizzle. Theresults of the tests were not used todetermine if these final rules wererequired, but rather to determine ifdesign changes were needed to preventa catastrophic roll upset. The rollcontrol testing and the AD’s must beviewed as two unrelated actions.

Comment 6. Request To Withdraw theProposals: Unsafe Condition is OutsideCertification Limits

One commenter states that theproposed AD’s should be withdrawnbecause the issuance of AD’s to addressthe problems of icing encountersoutside of the limits for which theairplane is certificated is a completelyinappropriate application of part 39 ofthe Federal Aviation Regulations (14CFR part 39). Another commentercontends that since the Aerospatialeaircraft passed all present certificationtesting, what transpired beyond thelimits of certification should not be heldagainst that aircraft.

The FAA does not concur that theAD’s should be withdrawn on the basisthat the unsafe condition is outside theicing certification envelope. Flight inicing conditions that are outside theicing certification envelope occursduring the normal service life of anairplane. Apart from the visual cuesprovided in these final rules, there is no


existing method provided to the flightcrews to identify when the airplane isin a condition that exceeds the icingcertification envelope. The appropriatevehicle for providing this method ofidentification is through issuance of anAD. The FAA acknowledges that theAerospatiale airplane has been shown tocomply with existing certification rules;however, no airplane is certificated forflight in icing conditions outside ofAppendix C of part 25 of the FederalAviation Regulations (14 CFR part 25).

Comment 7. Request To Withdraw theProposals: Proposals UnfairlyDiscriminate Against Turbopropeller-Powered Aircraft

Several commenters state that theproposed AD’s should be withdrawnbecause the AD’s unfairly discriminateagainst turbopropeller-powered aircraft.The commenters contend that by issuingthese proposed rules, the FAA iscreating a public perception thatturbopropeller-powered aircraft are lesssafe than other aircraft.

Numerous commenters oppose thestatement contained in the preamble ofthe proposals which indicates that sinceturbopropeller-powered airplanes aremore likely to operate at low altitudesand to make more frequent landings,they are more likely to encounter icingconditions that are outside the icingenvelope. One commenter states that themere fact that turbopropeller-poweredairplanes make more frequent landingsis irrelevant for the following reasons:—Every flight encounters the same

atmospheric conditions after takeoffand prior to landing, whether theairplane is powered by aturbopropeller or turbojet engine;

—There are numerous airplanespowered by turbojet engines thatoperate on segments equal in durationto those operated by manyturbopropeller-powered aircraft;numerous airplanes powered byturbojet engines make just as frequentlandings; and

—Even if turbopropeller-poweredaircraft do make more frequentlandings, there is no negativeinference to be drawn from that fact;more opportunities are available toensure that ice has not formed on theaircraft if the aircraft lands morefrequently.One commenter states that the

altitudes where SLD conditions exist arethe same altitudes at which jets wouldencounter those conditions during thedeparture and arrival phases of flight.Flight in SLD conditions that wouldhave a negative effect on aturbopropeller-powered airplane would

have the same effect on a jet, since bothare certificated under the same ruleswith regard to flight into adverseweather, and both fly at about the samespeeds during the departure and arrivalphases of flight. Additionally, anothercommenter adds that no airplane,whether it is powered by aturbopropeller, turbojet, or turbofanengine, is certificated for operation inSLD conditions.

Another commenter indicates thaticing encounters take place at altitudesbelow the cruising altitudes of mostturbopropeller-powered aircraft used inscheduled service; this also occurs onairplanes powered by turbojet engines.Icing encounters occur during takeoff,climb, descent, holding, and landingphases of flight on both types of aircraft.The commenter adds that operating theairplane in a holding pattern for aprolonged period in severe icingconditions is hazardous for both turbojetand turbopropeller-powered aircraft.The commenter explains that, althoughthe exposure time per flight hour of along-haul jet aircraft is less, theexposure on a per flight basis is exactlythe same. The commenter states that,like landing gear life limits, the propermeasure of exposure to freezing rain/freezing drizzle should be the number offlights, not the number of flight hours.

Another commenter, Saab, states thatSaab Model SAAB 2000 series airplaneshave a unique power-to-weight ratio,which makes it comparable withairplanes of the same size and, in somerelevant areas such as climbperformance and single engine ceiling,even far superior. Operators of thoseairplanes can operate the aircraft over-the-weather at flight level (FL) 310. Thismeans that these Saab airplanes operateon jet profiles and, therefore, are notexposed to the icing conditions that areoutside the icing envelope any morethan the airplanes that are excludedfrom the proposals.

The FAA does not concur that theproposals should be withdrawn. TheFAA does not intend to imply throughissuance of these AD’s thatturbopropeller-powered airplanes areless safe than airplanes having othertypes of propulsion systems. As statedin the preamble of the proposals, theFAA addressed certain airplanes as ahigher priority for two reasons:

—Turbopropeller-powered airplanes aremore likely to operate at low altitudesand to make more frequent landings;therefore, they are more likely toencounter icing conditions that areoutside the icing envelope specifiedin Appendix C of part 25 of the

Federal Aviation Regulations (14 CFRpart 25); and

—The flight crew of an airplane havingan unpowered roll control systemmust rely solely on physical strengthto counteract roll control anomalies,whereas a roll control anomaly thatoccurs on an airplane having apowered roll control system need notbe offset directly by the flight crew.Since the issuance of the proposed

rules, the FAA has reconsidered thisreasoning. The FAA acknowledges thatsimply because an airplane isturbopropeller-powered and has aparticular flight profile, that airplaneshould not be addressed as a higherpriority. However, this does notdiminish the significance of thenecessity of the flight crew of anairplane having an unpowered rollcontrol system to rely on physicalstrength to counteract roll controlanomalies. The subject airplanes allhave pneumatic deicing boots andunpowered aileron controls, which havebeen common denominators in theaccident and incident historyconcerning flight in icing conditionsand, in particular, during conditionswhen SLD was believed to be present.Therefore, airplanes having those designfeatures are of immediate concern to theFAA and were addressed as a higherpriority. Additionally, these AD’sprimarily address airplanes used inregularly scheduled passenger service inthe United States.

The FAA finds that the commentindicating that more frequent landingsprovides more opportunity to verify thatice has not formed is irrelevant. It alsocould be said that more frequentlandings gives more opportunity for iceto form. The FAA agrees with thestatement that holding for prolongedperiods in severe icing conditions ishazardous for all aircraft types. TheFAA is considering initiating anassessment of the need to prohibit allaircraft from continued flight in severeicing conditions as defined in theseAD’s.

Although Transport Canada Aviationdoes not request that the proposed AD’sbe withdrawn, the commenter indicatesthat roll control anomalies could existfor all aircraft whether they havepowered or unpowered roll controlsystems. Transport Canada Aviationadds that some jet-powered aircraft haveunpowered ailerons.

The FAA concurs that roll anomaliescould exist for all aircraft whether theyhave powered or unpowered roll controlsystems. However, these AD’s addressairplanes having both deicing boots andunpowered aileron controls. The FAA


acknowledges that other airplanes thathave powered ailerons may be subject toroll problems in severe icing conditionsdue to loss of lift. However, the FAA isnot aware of a mechanism that wouldallow ice to produce an uncommandedcontrol deflection on airplanes havingpowered flight control systems. Inaddition, airplanes having powered rollcontrol systems do not have directfeedback of aerodynamic forces to thepilot. However, the FAA is consideringinitiating an assessment of the need toapply similar limitations to otheraircraft types.

Comment 8. Request To Withdraw theProposals: Affected Airplanes Are NotSame Type Design as Accident Airplane

Several commenters contend that theproposals should be withdrawn becausethe FAA has not established clearly thatthe airplanes addressed in the proposedrules have the same type design as theAerospatiale Model ATR–72 seriesairplane that was involved in anaccident in October 1994 that occurredin severe icing conditions.

One commenter questions the words‘‘same type design,’’ and asks if thosewords refer to high wing, low wing, T-tail, or aircraft of another type design.

Three commenters providejustification in support of a request thatcertain airplanes be exempt from theseAD’s:

• de Havilland Model DHC–7 andDHC–8 series airplanes: De Havillandstates that the airplanes it manufacturesshare a conservative aerodynamicdesign philosophy that yieldsexceptional low-speed handlingqualities and demonstrated benignhandling qualities in icing conditions.De Havilland adds that two-thirds of theroll control authority of these airplanesis provided by hydraulically poweredroll spoilers. A second commenter addsthat increased testing has beenconducted on these airplanes.

• Fokker F27 Mark 100, 200, 300,400, 500, 600, 700, and 050 seriesairplanes: Fokker states that the leadingedge boots on Fokker Model F27 seriesairplanes and Model F27 Mark 050series airplanes extend to a chord wiseposition, 12.5 percent wing chord,which precludes all but the very largestdroplets impinging on the unprotectedsurfaces. Fokker adds that since theaccident airplane has unshielded hornbalances and the affected Fokkerairplanes do not have these unshieldedhorn balances, Fokker airplanes will notexperience roll upset problems. Fokkerindicates that aerodynamicallybalancing the control surfaces by meansof unshielded horn balances was notapplied because of the bad service

experience of the Vickers Viking aircraftin 1946.

• Beech Model 200 and 200Cairplanes: Raytheon states that theseparticular airplane models are notnormally considered to be commuteraircraft, and that issuance of an ADwould be contrary to the stated purposeof the proposals because most of theseairplanes are used in non-revenueservice. Raytheon states that theseairplanes are all low wing aircraft.Aerospatiale Model ATR–72 seriesairplanes (the accident airplane) is 50percent larger and carries over twice thenumber of passengers as these Beechaircraft. For these reasons, as well asother differences in the geometry of theairplanes (i.e., relative aileron span),Raytheon states that the supposition ofan icing hazard in these aircraft ispurely speculative.

The FAA does not concur that any ofthe addressed airplanes should beexempt from these AD’s. The FAA hasexamined the accident and incidenthistory in icing conditions and, inparticular, those events believed toinvolve SLD conditions. Results of thisexamination revealed that the typedesign characteristics that appear to becommon in these events are pneumaticdeicing boots and unpowered aileroncontrols. Airplanes having those typedesign characteristics appear to be moresusceptible to control problems insevere icing conditions. In response toFokker’s remark that its airplanes willnot experience roll control problemssince those airplanes do not haveunshielded horn balances, the FAA hasdetermined that horn balances on theaccident airplane were not the source ofthe uncommanded aileron motion.Design similarities of the wing, tail, orailerons do not appear to be a commondenominator among airplanes involvedin accidents or incidents where SLDconditions may have been present.

Saab asks for removal of the sentencethat reads, ‘‘Since an unsafe conditionhas been identified that is likely to existor develop on other airplanes of thesame type design . * * *’’ Saab statesthat this sentence implies that SaabModel SF340A and SAAB 340B seriesairplanes have a problem and that thisproblem is ‘‘likely to develop on otherairplanes of the same type design.’’ Yet,there have been no reported problemson those airplanes, which are not of thesame type design as all otherturbopropeller-powered airplanes.Transport Canada Aviation does notrequest that the proposals bewithdrawn; however, the commenterrequests that the FAA revise the samephrase discussed by Saab. TransportCanada Aviation requests that the

phrase be reworded as follows: ‘‘Sincean unsafe condition has been identifiedwhere aircraft icing certification is notadequate to address the conditions thatare outside of Appendix C of FAR part25 . . . .’’

The FAA does not concur with Saab’srequest. The FAA acknowledges thatthere have been no reported problemsinvolving severe icing conditions onSaab airplanes. However, Saab ModelSF340A and SAAB 340B seriesairplanes have pneumatic deicing bootsand unpowered aileron controls, whichhave been determined to be the commondenominators among the airplanesinvolved in accidents and incidents insevere icing conditions. Therefore, theFAA has determined that when severeicing conditions are encountered onthese Saab airplanes, those conditionsmust be exited.

Although the FAA has no technicalobjection to the revised wordingproposed by Transport Canada Aviation,this sentence does not reappear in thefinal rules. Therefore, no change to thefinal rule is necessary.

Comment 9. Request for Explanation ofthe Applicability of the AD’s

One commenter requests anexplanation of the methodology used bythe FAA to determine that AD’s shouldnot be issued for Cessna and Pipermulti-engine aircraft. The commenteralso asks if an AD similar to theproposed rules exists for Boeing Model737 series airplanes. The commenterindicates that Model 737 seriesairplanes have demonstrated abnormaland unexplained roll tendencies.

The FAA provides the followingclarification for this commenter. NoAD’s have been issued for Piperairplanes or Boeing Model 737 seriesairplanes. However, as reflected in thetable above, the FAA has issued an ADfor Cessna Model 208 and 208Bairplanes.

Most of the aircraft affected by thesefinal rules are used primarily inregularly scheduled passenger service inthe United States. However, there aresome airplanes affected by the finalrules that are not used in regularlyscheduled passenger service. Two ofthese are Cessna Model 208 and 208Bairplanes. Those airplanes wereincluded in the final rules because oftheir accident and incident history inicing conditions. The FAA isconsidering an assessment of the needto prohibit all aircraft from continuedflight in severe icing conditions.


Comment 10. Request To Withdraw theProposals: Service Experience ofAffected Airplanes is Satisfactory

Several commenters indicate that theFAA should withdraw the proposedAD’s in light of the satisfactory serviceexperience of the airplanes addressed inthe proposals. The commenters believethat the FAA is singling outturbopropeller-powered aircraft withoutany regard for the operational record ofthose aircraft.

Several commenters providejustification in support of this request:

• One commenter states that deHavilland airplanes have beensuccessfully operated for over 30 yearswithout one instance of roll upset orflight control problems.

• De Havilland indicates that deHavilland Model DHC–8 seriesairplanes have been in service for 11years and have accumulated 6 millionflights and 5 million flight hourswithout any incidents due to icing.

• De Havilland adds that deHavilland Model DHC–7 seriesairplanes have been in service for 18years and have accumulated 3.7 millionflights and 2.7 million flight hourswithout any incidents due to icing.

• Another commenter has notexperienced any icing related upsets orcontrol irregularities in its fleet of deHavilland Model DHC–8 seriesairplanes and Beech Model 1900 seriesairplanes.

• One commenter operates 21 BeechModel 1900D airplanes, 32 EMBRAERModel EMB–120 series airplanes, and41 Aerospatiale Model ATR–42 andATR–72 series airplanes; none of theseairplanes have experienced any icingincidents this season.

• One commenter indicates thatairplanes produced by Beech,EMBRAER, and Jetstream AircraftLimited (JAL) have no record ofuncommanded roll due to asymmetricalbuild-up of ice on surfaces beyond thedeicing boots.

• One commenter notes that it has notexperienced any unusual icingcharacteristics on its fleet of EMBRAERModel EMB–120 series airplanes andAerospatiale Model ATR–72 seriesairplanes.

• Fairchild notes that in over 26 yearsand 15,000,000 flight hours in passengerservice, there has never been a reportedincident where the controllability ofFairchild Aircraft SA226 and SA227series airplanes were in jeopardy as aresult of any icing encounters (includingSLD icing encounters).

• The Luftfartsverket (LFV), which isthe airworthiness authority for Sweden,states that no ice build-up behind the

wing boots has ever been reported onSaab Model SF340A, SAAB 340B, orSAAB 2000 series airplanes.Additionally, the leading edge on theseairplanes can be inspected easily duringflight.

• Saab remarks that no roll anomalyproblems in icing conditions haveoccurred during the extensive serviceexperience of Saab Model SF340A andSAAB 340B series airplanes.

• The FAA does not concur that theAD’s should be withdrawn. The fact thatan airplane has a perfect safety recordin icing does not negate the fact that noairplane has been certificated for flightinto SLD. The FAA has determined thata need exists to provide the flight crewwith useful safety-related informationregarding the limitations of the airplaneconcerning flight in severe icingconditions. The purpose of issuing thesefinal rules is to provide the flight crewwith such information.

One commenter, Transport CanadaAviation, requests that the proposalsapply only to those airplanes that havea demonstrated history of in-serviceproblems as a priority. The commenterstates that the hazards relating tooperation in icing conditions exist forall types of aircraft. (The commenterdoes not request that the proposed rulesbe withdrawn.)

The FAA does not concur with thisrequest. As explained previously, theFAA has issued AD’s for airplaneshaving pneumatic deicing boots andunpowered aileron controls as apriority. Airplanes having these designfeatures are of immediate concern to theFAA because these features have beencommon denominators in the accidentand incident history concerning flight inicing conditions and, in particular,during conditions when SLD wasbelieved to be present. The FAA isconsidering the need for rulemaking toimpose similar limitations on otheraircraft.

Comment 11. Request To Withdraw theProposals: Extensive Testing RevealedNo Icing Problems

Several commenters request that theproposals be withdrawn becauseextensive testing revealed no icingproblems on many differentturbopropeller-powered airplanes, eventhough those tests likely exceeded anyicing certification tests ever performedon other civil aircraft types, includinglarge jet-powered transport categoryairplanes. Fokker states that FokkerModel F27 series airplanes do notdemonstrate unacceptable roll controlcharacteristics in severe icingconditions; however, Fokker submits nodata to substantiate this statement.

The FAA does not concur. The FAAfinds that successful completion of theroll upset evaluation is not a validreason for withdrawing the AD’s. On thecontrary, if the evaluation haddemonstrated anomalies, the FAA mayhave concluded that action beyond thatrequired by these AD’s was necessary toaddress the demonstrated unsafecondition. The testing was designed toexamine only the roll handlingcharacteristics of the airplane in certaindroplets the size of freezing drizzle todetermine if any design changes arenecessary to prevent catastrophiccontrol surface deflection. The testingwas not a certification test to approvethe airplane for flight into freezingdrizzle since many of the componentsand their functions were not tested (e.g.,pitch control, engine and propeller,performance, stall warning, windshield,air data sensors and fuel system vents).Further, freezing rain was not tested.Satisfactory demonstration of those testsdoes not remove the FAA’sresponsibility to provide a safeoperating environment for thepassengers and crew.

JAL comments that its airplanes arenot subject to the addressed unsafecondition, and that the FAA hadconcurred with this contention. JALstates that the FAA agreed that, by thecontrollability evaluation process, allJetstream aircraft types had beendemonstrated to be not susceptible toroll control anomalies in freezing rain orfreezing drizzle conditions.

The FAA does not concur with JAL’sposition concerning its airplanes. AllJetstream airplanes affected by theseAD’s successfully completed the rollupset evaluation. However, as statedpreviously, no airplanes were tested infreezing rain conditions. The roll upsetevaluation only addressed conditionsthat were believed to have existedduring an accident involving a transportcategory airplane that occurred inOctober 1994. Therefore, since noairplane has been tested in all freezingrain and freezing drizzle conditions, noairplane has been demonstrated to besafe for continued flight in theseconditions.

Comment 12. Request To Withdraw theProposals: Publish Advisory Materialsand Require Training

Several commenters request that, inlieu of issuing the proposed rules, theFAA publish appropriate advisorymaterials and require training forrecognition, avoidance, and exit fromsevere icing encounters as part of therequired severe weather training forpilots and dispatchers. Two commenterssuggest that the FAA include such


requirements in the operating rulesspecified in part 121 (‘‘Certification andOperations: Domestic, Flag, andSupplemental Air Carriers andCommercial Operators of LargeAircraft’’) of the Federal AviationRegulations (14 CFR part 121). Anothercommenter indicates that, since jets andpiston-engine aircraft also coulddevelop ice shapes other than thosetested, training should not be providedonly to pilots of turbopropeller-poweredairplanes, but to pilots of all aircraft.Some commenters also suggest that theFAA has successfully addressed otherissues through increased awareness andtraining requirements, rather than byissuing AD’s against every airplane typedesign to require revising theLimitations Section of the AFM. Thecommenters cite windshear, grounddeicing, and clear air turbulence asexamples of such issues. Thecommenters contend that, except whereconfiguration changes are needed, suchas in the case of windshear detectiondevices, improved awareness andtraining programs—not AD’s—havebeen highly effective in achievingneeded safety improvements.

The FAA does not concur. The FAAconsiders that substituting advisorymaterial and mandatory training forissuance of an AD is not appropriate,nor would this adequately address theunsafe condition. The FAA fullysupports the development of advisorymaterials and training. Part 121(‘‘Certification and Operations:Domestic, Flag, and Supplemental AirCarriers and Commercial Operators ofLarge Aircraft’’) and part 135 (‘‘Air TaxiOperators and Commercial Operators’’)of the Federal Aviation Regulations (14CFR parts 121 and 135) require thatappropriate training concerninglimitations such as those contained inthese AD’s be incorporated into aircarriers’ training programs. However,the FAA’s position is that thedevelopment and use of such advisorymaterials and training alone are notadequate to address the subject unsafecondition. Currently, the AFM’s specifythat the affected airplanes arecertificated for flight in icing conditions;however, the AFM’s do not specify amethod of determining whether thecertification limits for those conditionshave been exceeded. Consequently, theFAA finds that these AFM’s must berevised to provide limitations for flightin icing conditions and to provide theflight crew with a method ofdetermining when those limitationshave been exceeded.

The FAA does not concur thatamending part 121 of the FederalAviation Regulations (14 CFR part 121)

in lieu of issuing these AD’s isappropriate. The FAA’s position is thatthe appropriate place to inform theflight crew of the limitations of theairplane is in the AFM. The appropriatevehicle for mandating such AFMrevisions is through issuance of an AD.In addition, an AD will ensure that theincorporation of such AFM revisions isnot left to each operator’s individualdiscretion and that flight crews receivepertinent information. The FAA mayconsider an assessment of the need toprovide training to pilots of all aircrafttypes for flight in severe icingconditions.

The commenters reference windshearas an example of an issue that washandled successfully without issuanceof an AD to revise the AFM’s. In thiscase, the AFM’s for all airplanes havingan onboard windshear system wererevised to provide the flight crew withprocedures for responding when thesystem gives an alert. Although no ADwas issued to mandate these AFMrevisions, without revising the AFM,operators could not comply with thesection of part 121 of the FederalAviation Regulations (14 CFR part 121)that requires installation of thewindshear detection devices. Inconclusion, although AFM revisionswere not required by an AD, AFMchanges were mandated indirectly by anew part 121 regulation.

The commenters also referenceground deicing. Part 91 (‘‘GeneralOperating and Flight Rules’’) of theFederal Aviation Regulations (14 CFRpart 91) prohibits takeoff of an airplaneunless the airframe is clear of ice;therefore, there is no need to provideadditional limitations concerning theamount of ice that would be acceptablefor takeoff. However, in the case ofsevere icing conditions addressed bythese final rules, the AFM’s currentlyallow flight in icing, but the AFM doesnot define when the limits of thecertificated icing operation envelopehave been exceeded.

Concerning the issue of clear airturbulence, issuance of an AD was notrequired because an airspeed limitationassociated with turbulent airpenetration was already in the AFM’s.Therefore, in this case, the issue wasaddressed in the AFM as well asthrough awareness and training.

Comment 13. Request To Withdraw theProposals: Incorporate OperationalIssues into a Training Curriculum

Two commenters request that theproposals be withdrawn because theproposed AD’s address an operationalissue that should be incorporated intoan operator’s training curriculum. One

commenter states that pilots must bemade aware of the hazards of icing andthat extended operation of an airplanein any icing encounter that results insignificant airframe accretion of ice isunacceptable.

The FAA does not concur that theAD’s should be withdrawn based on thecommenters’ request. The FAAacknowledges that these AD’s addressan operational issue. When therequirements of these AD’s areaccomplished and the AFM limitationsare revised, this material will beincorporated necessarily, as explainedpreviously, into the training curriculumfor the flight crews and dispatchers, ifapplicable, in the operator’s approvedtraining program. In this manner, pilotsand dispatchers, if applicable, will beinformed of the hazards of icing andthat continued operation of an airplanein certain icing conditions is prohibited.

Comment 14. Request To Withdraw theProposals: Require Training for AirTraffic Controllers and WeatherSpecialists

Two commenters request that theFAA implement additional policy torequire training for air traffic controllersand weather specialists in therecognition, avoidance, and proceduresto exit severe icing conditions.

The FAA does not concur that theseAD’s should be withdrawn. However,the FAA acknowledges thatimplementation of these AD’s maynecessitate additional training beyondthat which is already required for airtraffic controllers and weatherspecialists. The FAA may consider theneed to provide training concerningrecognition, avoidance, and proceduresfor exiting severe icing conditions.However, the intent of these AD’s is toprovide the flight crew with recognitioncues for, and procedures for exitingfrom, severe icing conditions. Theappropriate vehicle for requiring thatsuch information be included in theAFM’s is through issuance of an AD.

Comment 15. Request To Withdraw theProposals: Add a Caution to the AFM

One commenter requests that, in lieuof issuing the proposed AD’s, a‘‘Caution’’ should be added to the AFMto inform pilots to exit icing conditionsif ice was observed to be forming aft ofthe protected surfaces of the wings. Thecommenter states that informationregarding the use of flaps and theautopilot in icing conditions could alsobe incorporated into the AFM. Thecommenter does not indicate whichsection of the AFM should include thismaterial.


The FAA does not concur. The FAAfinds that the requirement to exit severeicing conditions and informationconcerning use of the autopilot duringflight in those conditions must beincluded in the Limitations Section ofthe AFM. Additionally, informationconcerning use of the flaps during thoseconditions should be included in theProcedures Section of the AFM. Theappropriate vehicle for requiring thesechanges to the AFM is through issuanceof an AD.

Comment 16. Request To Withdraw theProposals: Require Alternative AFMLimitation

One commenter requests that, in lieuof an AD, the FAA require an alternativeAFM limitation that reads as follows:‘‘This aircraft is certified for flight intoicing conditions as specified byAppendix C of Part 25. Actual icingencountered may be greater thanAppendix C requirements.’’

The FAA does not concur. Thesuggested limitation does not provideguidance as to how a pilot can identifyand safely exit icing conditions thathave exceeded those specified in theicing envelope in Appendix C of part 25of the Federal Aviation Regulations (14CFR part 25). These AD’s are intendedto provide the flight crew with visualcues which indicate that icingconditions have exceeded thecapabilities of the ice protectionequipment, and with procedures tosafely exit those conditions. No changeto the AD’s is necessary.

Comment 17. Request To Withdraw theProposals: AFM Revisions Already AreRequired

One commenter requests that theproposals be withdrawn because section121.133 (‘‘Manual Requirements:‘Preparation’ ’’) of the Federal AviationRegulations (14 CFR 121.133) alreadyrequires that operators incorporaterevisions into the AFM’s; therefore,issuance of the proposed AD’s isunnecessary.

The FAA does not concur. Section121.133 of the Federal AviationRegulations (14 CFR 121.133) does notspecifically require that AFM’s beupdated to current revisions. Section121.141 (‘‘Airplane or Rotorcraft FlightManual’’) of the Federal AviationRegulations (14 CFR 121.141) requiresthat the current AFM be carried on theaircraft, but does not requireincorporation of the most currentrevisions. Additionally, the commenterdoes not address the need to change theAFM’s for airplanes that operate underparts 135 (‘‘Air Taxi Operators andCommercial Operators’’) and 91

(‘‘General Operating and Flight Rules’’)of the Federal Aviation Regulations (14CFR parts 135 and 91). The appropriatevehicle for ensuring that the LimitationsSection of the AFM’s is changed isthrough issuance of an AD.

Comment 18. Request To Withdraw theProposals: Use Existing AFM Revisions

The General Aviation ManufacturersAssociation (GAMA), on behalf of itsmembers, states that some of theaffected manufacturers have preparedFAA-approved revisions for the AFM’sfor their products. GAMA indicates thatthose revisions incorporate specificinformation regarding cues forrecognizing severe icing conditions andprocedures for exiting such conditions,if encountered. Therefore, if theproposed AD’s are adopted, therequirements of the AD’s wouldsupersede the information operatorshave already incorporated into theAFM’s with less appropriateinformation that is not type designspecific.

One commenter, JAL, requests thatcertain existing AFM revisions for theaffected Jetstream airplanes be cited inthe proposed AD’s for those airplanes inlieu of the content of the proposed AD’s.(However, JAL does not request that theproposals be withdrawn for thisparticular reason.) JAL indicates that theexisting AFM revisions have alreadybeen FAA-approved.

The FAA does not concur with thecommenters’ requests. The FAAacknowledges that the AFM revisionsrequired by these final rules willsupersede previously approved AFMrevisions. However, the FAA is unawareof any AFM that addresses all of theprovisions specified in these final rules,nor of any AFM that contains specificvisual cues that the FAA has notincluded in the final rules. Even if AFMmaterial currently exists that doescontain all of the provisions of the finalrules, the FAA finds that issuance of anAD would still be necessary to mandatethe provisions of the AFM revisions.However, the FAA would consider arequest for approval of an alternativemethod of compliance, in accordancewith the provisions of this AD, for thoseoperators having AFM’s that alreadycontain all of the provisions of the finalrules.

Another commenter requests that theFAA withdraw the proposal that appliesto Fairchild Model SA226 and SA227series airplanes. The commenter statesthat the AFM for those airplanescurrently contains visual cues to aid theflight crew in recognition of weatherconditions conducive to SLD. This AFMalso provides procedures for avoidance

of such conditions. The commenteradds that these AFM procedures resultin additional operating limitations onthe aircraft with regard to severeweather conditions. The commenterbelieves these AFM procedures addressall current FAA requirements.

The FAA does not concur that theAFM for Fairchild Model SA226 andSA227 series airplanes addresses all ofthe proposed requirements of theproposed rule. For example, theLimitations section of the AFM for thoseairplanes does not require the flightcrew to exit severe icing conditions. Forthis reason, the FAA does not considerthe AFM for Fairchild Model SA226 andSA227 series airplanes to be equivalentto the information specified in theseAD’s.

Comment 19. Request To Withdraw theProposals: Develop Rulemaking toAddress Airplane Certification Outsideof Appendix C

Three commenters suggest thatinstead of arbitrarily prohibitingoperation of the airplane, the FAAshould undertake a well-designedresearch program and, if warranted,devise a rulemaking plan forcertification of airplanes outside ofAppendix C of part 25 of the FederalAviation Regulations (14 CFR part 25).One commenter also suggests possibleretroactive implementation of a newAppendix C.

The FAA does not concur because ofthe length of time that would berequired to implement the commenters’suggestion. The FAA finds that action isrequired prior to the commencement ofthe next icing season to prohibit thecontinued flight of airplanes in icingconditions that have been shown to beunsafe and for which the airplanes havenot been certificated. However, the FAAis currently considering initiating anassessment of the need to reviseAppendix C and the possibility of itsretroactive implementation.

Transport Canada Aviation states thatthe FAA has determined that there maybe a problem with the certificationrequirements for icing on de HavillandModel DHC–6, DHC–7, and DHC–8series airplanes, but not the specificapproval or design features of thoseairplanes. However, the commenterdoes not specifically request that theproposals be withdrawn.

The FAA does not concur with thecommenter’s statement. The FAA hasonly determined that no adequatemeans exists for the flight crew todetermine when the icing certificationlimits have been exceeded. The purposeof these AD’s is to provide more clearlydefined procedures and limitations


associated with severe icing conditions.This does not imply that thecertification requirements for icing areinadequate.

Comment 20. Request To Withdraw theProposals: Issue a ‘‘General AD’’ for AllAirplane Types

One commenter requests that a‘‘general AD’’ be issued to prohibit allairplane types from inadvertent flightinto hazardous SLD conditions. Anothercommenter adds that if encounters withfreezing rain/freezing drizzle conditionsmust be reported to Air Traffic Control,such reporting also should apply toflight crews of all airplane types.

The FAA does not concur with thecommenter’s request. For the reasonsdiscussed earlier in the preamble of thisAD, the FAA has determined thatairplanes having pneumatic deicingboots and unpowered aileron controlsare of immediate concern and have beenaddressed as a higher priority. The FAAfinds that action is required prior to thecommencement of the next icing seasonto prohibit the operation of theseairplanes in icing conditions that havebeen shown to be unsafe and for whichthe airplanes have not been certificated.However, the FAA is currentlyconsidering initiating an assessment ofthe potential adverse effects of SLD onall airplane types.

Comment 21. Request To Withdraw theProposals: Establish a DetailedReporting System

One commenter requests that the FAAestablish a detailed reporting system forinadvertent encounters with severe SLD.The commenter envisions a system thatwould provide a database for betteridentification of controllability issuesand visual indications related to theseencounters.

The FAA does not concur with thecommenter’s request. The FAA has beenadvised that the Regional AirlineAssociation (RAA) has alreadyestablished an ‘‘Unusual Icing ReportingProgram’’ for the purpose described bythe commenter; therefore, establishinganother reporting program wouldduplicate this benefit.

Comment 22. Request To Withdraw theProposals: Revise the Master MinimumEquipment List (MMEL)

Two commenters request that, insteadof addressing an MMEL item in an AD[i.e., the icing detection lightsreferenced in paragraph (a)(1) of theproposals], the FAA should require thatthe MMEL be revised. A thirdcommenter adds that the decision tochange the MMEL should be made byFAA Operations Inspectors based on

local conditions. One commenter statesthat the prohibition of dispatch withany inoperative ice detection lightswould preclude any efforts by anoperator to enhance safety by installinga second set of bulbs. The commenteradds that under this proposed rule, thistype of action would be penalized bysimply doubling the chances of aburned out bulb grounding the aircraft.In practice, if one were to add a fullyredundant set of bulbs, it wouldenhance safety by allowing theequivalent of the current illuminationlevel even with a bulb burned out.

The FAA does not concur with theserequests. FAA Operations Inspectors arenot authorized to make MMELrevisions. The FAA has determined thatit is prudent to address the icingdetection lights in these final rules toensure uniform and immediateapplication of the requirements of theAD’s. Concerning the example providedby one of the commenters, if an operatorchooses to add a fully redundant set ofbulbs, that operator should requestapproval of an alternative method ofcompliance in accordance with theprovisions of this final rule.

Although Transport Canada Aviationdoes not request that the proposals bewithdrawn, it requests a revision to therequirement that all icing detectionlights must be operative. For deHavilland Model DHC–7 and DHC–8series airplanes, the commenter requeststhat the requirement be changed tomandate that at least one outboard andone inboard inspection light beoperative prior to flight into known orforecast icing conditions at night. Sincethe MMEL contains a provision that asuitable lamp/light of adequate capacitybe available, this is consideredacceptable in conjunction with otherindications of freezing rain or freezingdrizzle. Similarly, for de HavillandModel DHC–6 series airplanes, therequirement should be revised torequire a suitable lamp/light fordispatch at night with one winginspection light inoperative.

The FAA does not concur. The FAAhas determined that the justificationprovided by the commenter is notadequate to enable the FAA todetermine if the proposed changes areacceptable. During severe icingconditions, the flight crew’s workloadmay be high, and there may be noopportunity to use the portable lamp/light, which, in itself, may createdisorientation in the cockpit due toadverse reflections from the glass. TheFAA’s intent in having all inspectionlights be operative at night is to providethe flight crew the best possiblevisibility of the airframe. However, the

FAA would consider a request forapproval of an alternative method ofcompliance, in accordance with theprovisions of these AD’s, provided thatadequate justification is presented tosupport such a request.

Comment 23. Request To Withdraw theProposals: Certify Airplanes for Flight inConditions Outside Appendix C

One commenter implies that theairplanes affected by the proposed rulesmust be rectified to a level beyond thepresent certification requirements forflight in icing.

The FAA does not concur. The finalrules do not require certification of theairplane beyond the current certificationrequirements for flight in icing specifiedin Appendix C. These AD’s simplyprovide the flight crew with visual cueswhich indicate that icing conditionshave exceeded the capabilities of the iceprotection equipment, and withprocedures to safely exit thoseconditions.

One commenter requests that theproposal for de Havilland Model DHC–6 series airplanes be withdrawn becausethis airplane model is type certificatedin Canada, which is a country with ahigher standard than the United Statesfor operating in icing conditions.

The FAA does not concur. Thiscommenter did not submit data to theFAA to substantiate that the airplanehas been shown to be safe for flightoutside the icing certification envelopespecified in Appendix C. Additionally,the FAA is unaware of any foreign civilaviation authority having certificationrequirements for icing conditions thatare outside of the icing certificationenvelope used in the United States.

Comment 24. Request To Withdraw theProposals: Proposals Prohibit Takeoff orApproach in ‘‘Light Freezing Drizzle’’Conditions

One commenter requests theproposals be withdrawn because theproposed limitation would prohibittakeoff or approach when ‘‘light freezingdrizzle’’ conditions that are caused bylight precipitation falling through a thinlayer of cold surface air below warmerair above are reported on the surface.The commenter maintains that withaccomplishment of the appropriateground deicing precautions prior totakeoff, no hazard to the operation of theairplane is posed.

The FAA does not concur that theAD’s should be withdrawn for thisreason. These AD’s do not affect anyexisting regulations or FAA-approvedoperating procedures related to takeoff,dispatch, or release of an airplane inicing conditions, nor do these AD’s


prohibit operation in specificmeteorological conditions. These AD’sonly prohibit remaining in icingconditions when certain visual cues arepresent on the airplane. Operators mustcomply with existing rules that requirean airplane to be free of ice prior totakeoff. Therefore, takeoff in ‘‘lightfreezing drizzle’’ would only beprohibited by existing regulations orFAA-approved operating procedures,not by these AD’s. As explainedpreviously, the FAA considers thatlanding the airplane when freezing rain/freezing drizzle conditions areencountered would, in many cases, bethe most expeditious method of exitingthe conditions. Such landing would bein compliance with the limitation thatrequires the flight crew to exit thesevere icing conditions.

Comment 25. Request To Withdraw theProposals: Proposals Leave UnansweredQuestions

One commenter contends that theproposals leave unanswered questions.The commenter alleges that without theanswers to those questions, affectedparties are deprived of the ability toprovide informed comments and,thereby, are ‘‘denied their rights underthe Administrative Procedures Act(APA) to comment on the proposedrules.’’ Specifically, the commenterasks:—What is unusual icing?—Does the pilot, Air Traffic Control,

dispatch, or the FAA determine whenthe conditions exist?

—What is splatter effect?—Where are the operating instructions

incorporated—in the AFM, trainingmanuals, or some other document?

The FAA infers from the commenter’sremarks that the commenter requests theproposed AD’s be withdrawn becauseinformed comments could not beprovided.

The FAA does not concur that theAD’s should be withdrawn on this basis.The FAA does not agree that the publichas been deprived of the ability toprovide informed comments, asrequired by the APA. In general, theAPA requires that notice of the terms orsubstance of a proposed rule bepublished in the Federal Register. Thepurpose of this requirement is to ensurethat federal agencies thoroughlyconsider all information and opinionssubmitted by the public before anyrequirements are imposed. Notice isintended to improve both the quality ofthe regulations and their acceptability tothe public. The FAA finds that none ofthe questions raised by the commenteridentify areas in which the commenter

has not been provided a reasonableopportunity to comment. The fact thatthe commenter raises questions suggeststhat the commenter considers a need forfurther clarification. Even if thecommenter is correct in that thesequestions require clarification, that factin itself is a comment that can beaddressed properly by simply clarifyingterms. The fact that clarification isnecessary does not mean that the publichas been denied reasonable opportunityto comment.

In response to the commenter’squestions, the FAA provides thefollowing clarification. The term‘‘unusual icing’’ did not appear in theproposed rules. However, the phrase‘‘unusually extensive ice’’ is referencedin paragraph (a)(1) of the final rules.[This reference appears in paragraph(a)(2) of the final rule for Aerospatialeairplanes.] ‘‘Unusually extensive ice’’accrued on the airframe in areas notnormally observed to collect ice is avisual cue that is subject tointerpretation by the flight crew;therefore, a specific definition of‘‘unusually extensive ice’’ cannot beprovided.

These AD’s address changes to AFMlimitations, which pertain to the pilotsince the pilot is responsible to look forthe visual cues defined in the AD’s.Therefore, the pilot determines whensevere icing conditions exist.

The terminology ‘‘splatter effect’’ didnot appear in the proposed rules. TheFAA infers from the commenter’squestion that the commenter isreferencing terminology used inparagraph (a)(2) of the proposed AD’s.‘‘Droplets that splash or splatter onimpact at temperatures below +5degrees Celsius OAT’’ is a visual cuethat was included in the proposed AD’sas a method of identifying severe icingconditions.

Concerning incorporation of operatinginstructions, these final rules specifythat the AFM’s be revised. The AD’s donot specify that any other manuals ordocuments be revised. However,information that is included in the AFMas a limitation is necessarily included inthe training program.

Comment 26. Request To Clarify Scopeof Icing Conditions Addressed

Transport Canada Aviation suggeststhat the proposals, which address onlyfreezing rain/freezing drizzleconditions, are not adequate to cover allhazards related to operation of aircraftin icing conditions. The commentermakes no specific request.

The FAA concurs that these AD’s donot address all icing related hazards.The FAA’s intent is to minimize the

potential hazards associated withoperating the airplane in severe icingconditions by providing the flight crewswith more clearly defined proceduresand limitations associated with suchconditions. However, no change to thefinal rules is necessary.

Comment 27. Request To Expand theApplicability of the AD’s

One commenter, the CAA, suggeststhat the ‘‘coverage’’ of the proposalsshould be stated clearly. The CAAbelieves that a restriction to thoseoperations in ‘‘regularly scheduledpassenger service’’ is not warranted fora safety issue as it does not cover cargo,charter, or private operations. Thecommenter does not specify whichairplane models should be addressed.The FAA infers from the commenter’sremarks that it requests that theproposed AD’s be applicable to otherairplane models that are used in cargo,charter, or private operations that mayhave been excluded from theapplicability of these AD’s.

The FAA does not concur that theapplicability of these AD’s should beexpanded to include additional airplanemodels used primarily in cargo, charter,or private operation. The FAA iscurrently considering the need foradditional rulemaking to address otherairplane models having pneumaticdeicing boots and unpowered aileroncontrols that are used in these types ofservice that were not addressed by theseAD’s. Additionally, the applicability ofthese final rules indicates that the AD’sapply to ‘‘all’’ of the airplane modelsidentified, certificated in any category.This means that the AD’s apply to all ofthe affected airplanes, regardless of howthose airplanes are operated (includingpassenger service, cargo, charter, orprivate operation).

Comment 28. Request for DesignChanges to the Airplanes

One commenter requests that the FAArequire design changes to the airplanes,which, when accomplished, will allowelimination of the AFM limitations. Thecommenter states that abnormal rollcontrol anomalies could be eliminatedby design changes that prevent any iceshapes from forming by usingsupplemental ice protection added toexisting pneumatic boots or other iceprotection installations. The commenterconcludes that, given this addedprotection, restricting flight in freezingdrizzle could be reduced to allowexposure to these atmosphericconditions for a reasonable time andwould not require immediately exitingthese conditions when encountered aspresently stipulated.


The FAA does not concur that itshould require design changes toairplanes in these AD’s. Currently, theFAA is unaware of any design changesthat would allow elimination orreduction of the AFM limitationsspecified in these AD’s. However, ifsuch design changes are developed,approved, and become available, theFAA would consider additionalrulemaking to require such changes. TheFAA finds that even if the ice protectionsystem prevented the formation of iceshapes in front of the ailerons when theairframe is exposed to certain freezingdrizzle conditions, other meteorologicalconditions still exist (e.g., freezing rain)for which the airplane would not becertificated.

Comment 29. Request for More SpecificVisual Cues

One commenter requests that the FAAprovide more specific visual cues foridentification of freezing rain or freezingdrizzle conditions. The commenterstates that the generic visual cuesprovided in the proposed AD’s are notadequate for aircraft types thatfrequently operate in and encounterSLD conditions. For example, ice couldbe forming on the upper wing and notthe lower wing; therefore, looking at thelower wing would not be a reliablevisual cue. Two commenters suggestthat specific visual cues be provided foreach airplane model. One of thesecommenters states that subjective cuesmay be of limited benefit if the pilot’sexperience with icing is inadequate. Theother commenter adds that subjectivevisual cues will result in varyinginterpretations (i.e., some unnecessarycourse changes in altitudes or serviceinterruptions caused by overlyconservative interpretations). TransportCanada Aviation does not request morespecific visual cues; but states that‘‘unusually extensive ice,’’ ‘‘normallyobserved,’’ and ‘‘farther back thannormally observed’’ are all variableterms that are largely dependent onflight crew experience. The commentercontends that limitations andprocedures described using these termswill not be consistently interpreted. Inaddition, Transport Canada Aviationstates that ice on the lower wing surfaceaft of the protected area, by itself, isunlikely to cause a hazard. Moreover,the presence or absence of such icecannot be used as an indication of anyhazardous accumulation on the upperwing surface or on the horizontalstabilizer.

The FAA does not concur with thecommenters’ request to provide morespecific (or airplane-specific) visualcues. The FAA agrees with the

commenters’ assertion that, undercertain circumstances, examination ofthe undersurface of a high wing may notbe reliable. The FAA also agrees thatother cues, such as unusually extensiveice accrued on the airframe in areas notnormally observed to collect ice andaccumulation of ice on the propellerspinner farther aft then normallyobserved, are subjective and thatreliance on pilot judgment andexperience is necessary in such cases.Additionally, the FAA fully supportsthe development and use of airplane-specific cues by operators andmanufacturers. Unfortunately, nocommenter provided airplane-specificcues during this comment period.

In summary, the FAA finds that thecombined use of the generic cuesprovided and the effect of the final rulesin increasing the awareness of pilotsconcerning the hazard of operatingoutside of the certification icingenvelope will provide an acceptablelevel of safety. However, for thoseoperators that elect to identify airplane-specific visual cues, the FAA wouldconsider a request for approval of analternative method of compliance, inaccordance with the provisions of thisAD.

Transport Canada Aviation states thatthe term ‘‘protected area’’ may not bereadily recognizable by the flight crew;for example, not all of a deicing bootsurface is ‘‘protected area.’’ [Thisterminology appears in the secondvisual cue (in the proposals forairplanes other than Aerospatialeairplanes) and in the autopilotlimitation in paragraph (a)(1) of theproposals. For Aerospatiale airplanes,this terminology appears in thesecondary indications in paragraph(a)(1) of the proposal.] The FAA infersthat the commenter requests that morespecific language than ‘‘protected area’’be used.

The FAA does not concur that thisterminology should be revised. TheFAA considers that a pilot understandsthat a portion of the deicing boot wouldbe considered to be unprotected.Therefore, no additional clarification ordefinition of the term ‘‘protected area’’is necessary.

Comment 30. Request to Reference ClearIcing Conditions and Clear Componentof Mixed Icing Conditions

One commenter also asks that allreferences to freezing rain and freezingdrizzle environments and visual cueidentification reference clear icingconditions and the clear component ofmixed icing conditions. According tothe commenter, mixed icing conditionscan contain areas of freezing rain and/

or freezing drizzle. The commenternotes that mixed icing has taken on twodifferent definitions within the aviationcommunity—the ‘‘engineering’’definition (which is defined in an FAAicing handbook) and the definitionpilots use (which includes areas of clearand rime ice). The commenter statesthat a clear definition of theseconditions is needed. The commenteradds that only pilot reports can showthat freezing rain/freezing drizzle existsbecause forecasting of these conditionsis inadequate. The commenter indicatesthat while the Aerospatiale airplaneshave side window cues that willaccurately identify freezing rain orfreezing drizzle, pilots of other airplaneswithout such a sophisticated cue mayerroneously report mixed icing.

The FAA does not concur. The FAAacknowledges that freezing rain andfreezing drizzle may be reported asclear/mixed icing conditions. However,the flight crew must exit icingconditions that produce the visual cuesspecified in the final rules. Exiting theicing conditions is not dependent uponthe terminology used to describe theconditions. Therefore, the FAA hasdetermined that it is not necessary toinclude references to clear icingconditions and the clear component ofmixed icing conditions. In addition, theFAA has determined that including adiscussion in these AD’s of thephenomenon of mixed icing conditionsas it relates to the current state-of-the-artweather forecasting would be prematurebecause no clear definition of thisphenomenon has been agreed uponamong the aviation community. TheFAA is currently considering anassessment during which various icing-related subjects, including mixed icingconditions, would be addressed.

Comment 31. Request for Research andUse of Wing-Mounted Ice Detectors

One commenter requests that wing-mounted ice detectors, which providereal-time icing severity information (orimmediate feedback) to flight crews,continue to be researched and usedthroughout the fleet. The FAA infersfrom this commenter’s request that thecommenter asks that installation ofthese ice detectors be mandated by theFAA.

While the FAA supports thedevelopment of such ice detectors, theFAA does not concur that installation ofthese ice detectors should be required.The specifications for automaticdetectors having the capabilities todifferentiate among freezing rain,freezing drizzle, and other icingconditions have not been determined.However, if such ice detectors are


developed, approved, and becomeavailable, the FAA may consider furtherrulemaking action to require installationof such equipment.

Comment 32. Request to Limit theApplicability of the AD’s

One commenter requests that theapplicability of the proposals be limitedto airplanes having NACA 430xxairfoils. The commenter asserts that theunusual pressure peak on the NACA430xx airfoils at 9 percent chord causedthe ice ridge to form at that point, whichresulted in the accident involving aAerospatiale Model ATR–72 seriesairplane. The commenter states that‘‘the accident was caused by the poorlydesigned, unusual, and fortunatelyrarely used NACA 430xx airfoils usedon this airplane.’’

The FAA does not concur with thecommenter’s request to limit theapplicability of the AD’s. First, theNational Transportation Safety Board(NTSB) has not yet made an officialfinding of the probable cause of theaccident referenced by the commenter.Therefore, the FAA cannot assume thatairplanes having NACA 430xx airfoilsare more susceptible to the addressedunsafe condition than those airplanesthat do not have this type of airfoil.Second, the FAA has examined the datasubmitted by the commenter, anddisagrees with the commenter’sassertion concerning the formation ofice ridges. The formation of ice ridgesdepends on many factors. Ice ridgeshave been observed to form in areaswhere there is no pressure (commonly,‘‘suction’’) peak. However, theimpingement location of large dropletsis more relevant to the development ofice ridges than the particular pressuredistribution. The commenter does notaddress the fact that, regardless of thetype of airfoil on an airplane, asubstantial sharp edge protuberance inthe vicinity of the suction peak can haveadverse consequences to theaerodynamic performance of the airfoil.Regardless of the cause of location of iceformations, prevention or removal of theice is certainly an acceptable remedy forsuch conditions, should thoseconditions occur. For example,Aerospatiale extended the deicing bootsto prevent the formation of adverse iceridges.

Comment 33. Request for Approval ofImproved Deicing Equipment forAerospatiale Airplanes

ATR requests that paragraph (b) of theproposed rule for Aerospatiale airplanesbe revised to indicate that installation ofany improved version of deicingequipment that is approved by the FAA

is acceptable for compliance with therequirements of that paragraph. Thecommenter provides no justification forits request.

The FAA does not concur with thecommenter’s request to revise the AD.However, if an improved version ofdeicing equipment is developed,approved, and available, the FAA wouldconsider a request for approval of analternative method of compliance, inaccordance with the provisions of theAD.

Comment 34. Request for Re-Evaluationof Modified Deicing Boots onAerospatiale Airplanes

In response to the proposal forAerospatiale airplanes, one commenterrequests that the new, enlarged deicingboots that are required to be installed onthese airplanes must be re-evaluatedbefore total confidence in the modifiedboots is warranted. The commenterasserts that no test data exist to showthat the modified boots will precludethe problem of large droplets outside ofAppendix C. The area of exposureoutside of Appendix C is essentiallyopen-ended, and only limited testingwithin a narrow range of dropletdiameters was conducted. Additionally,the test conditions that existed duringthe tanker testing conducted at EdwardsAir Force Base, which was intended tobe a ‘‘before modification/aftermodification’’ validation program, werenot identical. The commenter adds thatno modification will ensure that anyairplane is safe while flying in icingconditions outside those specified inAppendix C.

The FAA does not concur with thecommenter’s request for a re-evaluationof the modified deicing boots. Themodified deicing boots for theseairplanes were subjected to an extensivecertification program by both the FAAand the Direction Generale de l’AviationCivile (DGAC), which is theairworthiness authority for France. FAAapproval of the modified boots wasbased on engineering analyses, windtunnel testing, flight testing in naturalicing conditions, and a validationprogram involving a United States AirForce icing tanker. This testing verifiedthat the modified boots continue toperform the intended function withinthe Appendix C icing envelope. Inaddition, the extended deicing bootswere shown to adequately protect theairplane from the larger, supercooledwater droplets that are believed to haveexisted in the area at the time of theaccident in October 1994.

It should be noted, however, that it isnot intended that the modified bootsprovide protection in all possible icing

conditions, including freezing rain/freezing drizzle. However, the FAAconsiders that the combination of theenlarged deicing boots, the AFMoperational procedures and restrictions,and the visual cues which indicate entryinto freezing rain/freezing drizzleconditions provides for an enhancedlevel of safety during inadvertent flightin these conditions.

Comment 35. Request for FormalWeather Forecasting System forFreezing Rain/Freezing Drizzle

One commenter supports arequirement to establish a formal systemto provide forecasts of freezing rain/freezing drizzle conditions, as proposedin paragraphs (b) and (c) of the originalproposed rule for Aerospatialeairplanes. [This proposed requirementwas removed from the subsequentsupplemental notice of proposedrulemaking (NPRM) issued for theseairplanes in January 1996.] Thecommenter states that such arequirement should remain in effectuntil forecasting tools are developed ordetection methods are established toprevent dispatch or operations inconditions outside those specified inAppendix C. The commenter states thatthe efficacy of the deicing boots has notbeen shown completely nordocumented; therefore, avoidance offreezing rain/freezing drizzle isparamount to safety of flight.

The FAA does not concur that such arequirement is necessary. The FAAagrees that such a system wouldenhance the safety of flight operations.However, there is no evidence that lackof a system with such specializedfeatures would lead to an unsafecondition. Forecasts of freezing rain/freezing drizzle are a normal part of pre-flight weather briefings. The FAA isaware, however, of serious limitationsfor such a system to provide accurateand timely forecasts of these conditionsduring flight in areas that are removedfrom weather reporting stations. Quiteoften, the only indication of theexistence of severe icing conditions isfrom pilot reports or other directobservations.

Research is underway currently inindustry and the academic communityto address shortcomings in theforecasting of severe icing conditions.The FAA may consider furtherrulemaking if advancements in weatherforecasting provide for a reliable methodto predict the occurrence of freezingrain/freezing drizzle conditions duringflight or in areas removed from directobservations.


Comment 36. Request To ApproveEarlier Service Bulletin Revisions

One commenter to the proposed rulefor Aerospatiale airplanes requests thatthe proposed AD be revised to specifythat earlier revisions of service bulletinsare acceptable for compliance with therequirements of the proposed rule. Thecommenter makes this request so as toeliminate the need to apply for approvalof alternative methods of compliancewhen accomplishing service bulletinrevisions other than those specified inthe proposed rule.

The FAA does not concur that earlierrevisions of the referenced servicebulletins should be cited in the finalrule for Aerospatiale airplanes.However, the FAA would consider arequest for approval of an alternativemethod of compliance, in accordancewith the provisions of the AD, providedthat adequate justification is presentedto support such a request.

Additionally, the FAA has revised therevision levels specified for certainservice bulletins because those revisionlevels were omitted inadvertently fromparagraph (b) of the proposed rule forAerospatiale airplanes. That final rulehas been revised to indicate that certainmodifications are to be accomplished inaccordance with Revision 1 ofAerospatiale Service Bulletins ATR42–57–0043, ATR72–57–1015, and ATR72–57–1016. The correct date for Revision1 of those service bulletins (April 10,1995) was specified in the proposal forthe affected airplanes.

Comment 37. Request To ReviseReferenced Service Bulletins

One commenter to the proposal forAerospatiale airplanes suggests thatservice bulletin revisions shouldcontain a statement indicating that therevision has no effect on previouslymodified airplanes. The commenterprovides no justification for this request.

The FAA acknowledges that manyservice bulletins do contain thesuggested phrase as an aid to operatorsthat may already have accomplished anearlier service bulletin revision. In fact,if a particular service bulletin isspecified in an AD and that servicebulletin is revised, the FAA routinelydetermines whether the service bulletinrevision adequately addresses theunsafe condition specified in the AD; ifnecessary, the FAA amends the AD tocite the later service bulletin revision.

Comment 38. Request To Revise VisualCue: Ice on Side Window

One commenter suggests revisedwording for the first visual cue specifiedin paragraph (a)(1) of the proposed rule

for Aerospatiale airplanes, as follows:‘‘Freezing rain and freezing drizzle arecharacterized by ice covering all or asubstantial part of the unheated portionof either forward side window and/orwater splashing or streaming on thewindshield or the side window when infreezing or near freezing temperatures.’’The commenter states that the presentwording implies that ice will alwaysappear on the side window; however,this is not the case.

The FAA does not concur with thecommenter’s request. The commenter’srevised wording suggests that watersplashing or streaming on thewindshield or the side window wouldbe a primary cue used to determinewhen severe icing conditions arepresent. The FAA does not concur thatwater splashing or streaming on thewindshield or the side window wouldbe a reliable cue in itself. However, thiscue may be used as a supplemental cueto the primary cue of ice accruing on theside window. No change to the finalrule for Aerospatiale airplanes isnecessary.

Comment 39. Request To Remove VisualCue: Unusually Extensive Ice Accretion

One commenter, Saab, requests that ifthe FAA does not withdraw theproposed AD’s, paragraph (a)(1) of theproposal for Saab SF340A and SAAB340B series airplanes should be revised.The commenter suggests that the firstvisual cue that appears in thatparagraph, which relates to unusuallyextensive ice accretion, be removedfrom the proposal for those airplanes.Saab indicates that critical ice isbelieved to be ice that builds up beyondthe protected surfaces on the wing. OnSaab Model SF340A and SAAB 340Bseries airplanes, the pilot has a goodview of the outer wing and the propellerspinner. Unusually extensive ice inother areas may or may not besignificant in determining whetherfreezing rain or freezing drizzle ispresent; however, the primary visualcue for these airplanes is ice on thespinner/outer wing.

In light of Saab’s remarks, the FAAconcurs that the visual cue addressed bythe commenter should be removed fromthe final rule for Saab Model SF340Aand SAAB 340B series airplanes. (Thatvisual cue remains in place for SaabModel SAAB 2000 series airplanes.)Paragraph (a)(1) of that final rule hasbeen revised accordingly.

A second commenter, Raytheon,requests that the same visual cue beremoved from the proposal for Beechairplanes. Raytheon indicates that itdoes not believe that observation of thisvisual cue indicates that the airplane

has exceeded the Appendix C icingenvelope with respect to Beechairplanes. Therefore, the cue specifiedin the proposal would be irrelevant inan AFM for these airplanes.

The FAA does not concur withRaytheon’s request. The commenter hasnot submitted data to warrant removalof the visual cue. No change to the finalrule for Beech airplanes has been made.

Comment 40. Request To Remove VisualCue: Accumulation of Ice on WingSurfaces

JAL requests that the FAA remove thegeneric information contained in thevisual cue concerning accumulation ofice on the wing surfaces from theproposals for Jetstream airplanes. JALindicates that, for its airplanes, theappropriate visual cue is the accretionof ice behind the protected area of thewing upper surface (not the wing lowersurface).

The FAA concurs. The FAA finds thatthis particular visual cue should beairplane-specific. Therefore, the FAAhas customized paragraph (a)(1) of thefinal rules for all affected airplanes tospecify whether accumulation of ice isobserved on the upper or lower surfaceof the wing, depending upon whetherthe airplane is a high- or low-wingairplane. [Operators should note that,for Aerospatiale airplanes, the cue wascustomized in paragraph (a)(2) of thefinal rule.]

Comment 41. Request To Revise VisualCue: Accumulation of Ice on PropellerSpinner

One commenter requests that the FAArevise the visual cue concerningaccumulation of ice on the propellerspinner, as specified in paragraph (a)(1)of the proposals. For consistency, thecommenter requests that the word‘‘back’’ be replaced with ‘‘aft.’’

The FAA concurs with thecommenter’s request. The final ruleshave been revised to change the visualcue to read as follows: ‘‘Accumulationof ice on the propeller spinner fartheraft than normally observed.’’ [Operatorsshould note that, for Aerospatialeairplanes, this change appears inparagraph (a)(2) of the final rule.]

Comment 42. Request To Remove VisualCue: Accumulation of Ice on PropellerSpinner

One commenter, JAL, requests thatthe FAA remove the visual cueconcerning accumulation of ice on thepropeller spinner from the proposals forJetstream airplanes. JAL indicates thaton Jetstream Model ATP airplanes andModel 748 series airplanes, thepropeller spinner is not visible from the


flight deck. On Jetstream Model 3101,3201, and 4101 airplanes, the propellerspinner is visible from the flight deck,but flight test experience indicates thatthere is no unique correlation betweenthe extent of spinner ice accretion andthe existence of freezing rain/freezingdrizzle conditions.

The FAA concurs partially. The FAAconcurs that since the propeller spinneris not visible from the flight deck onJetstream Model ATP airplanes andModel 748 series airplanes, the visualcue can be removed from paragraph(a)(1) of the final rules for these models.The FAA does not concur that thisvisual cue should be removed from theAD’s for Jetstream Model 3101, 3201,and 4101 airplanes. The commenter didnot submit data to substantiate itsassertion that flight test experienceindicates there is no unique correlationbetween the extent of spinner iceaccretion and the existence of freezingrain/freezing drizzle conditions.Therefore, it is uncertain if thecommenter’s flight test airplane wasequipped with instrumentation thatwould allow the detection and/ormeasurement of droplets outside theAppendix C conditions, and if theairplane had flown into icing conditionscontaining freezing rain or freezingdrizzle.

Comment 43. Request To RemoveLimitation to Immediately Exit FreezingRain/Freezing Drizzle

Saab requests that the FAA remove asentence from paragraph (a)(1) of theproposals that requires the pilot toimmediately exit freezing rain orfreezing drizzle conditions by changingaltitude or course. This commenterpoints out that the first limitationcontained in the proposal for Saabairplanes (‘‘Flight in meteorologicalconditions described as freezing rain orfreezing drizzle, as determined by thefollowing visual cues, is prohibited* * *’’) already prohibits flight in theseconditions, and the pilot shouldrespond accordingly. Raytheon believesa conflict exists between usingobservations of ice accretion, asrequired by paragraph (a)(1) of theproposed rules, and the‘‘determination’’ of certainmeteorological conditions.

The FAA concurs partially. The FAAdoes not agree that the sentencediscussed by Saab should be removedfrom paragraph (a)(1) of the final rules.As explained previously, the firstlimitation in paragraph (a)(1) of the finalrules has been revised to read: ‘‘Duringflight, severe icing conditions thatexceed those for which the airplane iscertificated shall be determined by the

following visual cues. If one or more ofthese visual cues exist, immediatelyrequest priority handling from AirTraffic Control to facilitate a route or analtitude change to exit the icingconditions.’’ (This wording is slightlydifferent in the final rule forAerospatiale airplanes because only onevisual cue is provided.) The FAA findsthat this revision to the final rulesaddresses the commenters’ concernswith regard to the proposed limitations.

One commenter poses variousquestions concerning the last sentenceof the first instruction listed in theprocedures for exiting the freezing rain/freezing drizzle environment inparagraph (a)(2) of the proposals. (Thatsentence reads as follows: ‘‘Asking forpriority to leave the area is fullyjustified under these conditions.’’)—What does the term ‘‘priority’’ provide

a pilot when asking for priority toleave icing conditions?

—What if there were three simultaneousrequests for ‘‘priority?’’

—What Air Traffic Control proceduresexist for treating an immediate requestfor ‘‘priority?’’

—Where is the term ‘‘priority’’ defined?The commenter states that confusionover terms that have not been definedclearly by the FAA has partially resultedin accidents and incidents. However,the commenter does not cite a specificcase in which this occurred.

The FAA has re-examined the lastsentence of the first instruction listed inthe procedures for exiting the freezingrain/freezing drizzle environment inparagraph (a)(2) of the proposals. TheFAA has reconsidered use of the term‘‘priority.’’ The FAA finds that moreappropriate language that would beunderstood clearly by the flight crewand Air Traffic Controllers should beused in that instruction. Existingtraining for flight crews and Air TrafficControllers addresses priority handlingof airplanes. However, the FAA willissue additional information for AirTraffic Controllers to further clarifypriority handling of airplanes in severeicing conditions. The FAA finds that thelimitations specified in paragraph (a)(1)of the final rules will result in the pilottaking appropriate steps to exit the icingconditions. Therefore, the FAA findsthat the sentence questioned by thecommenter may be removed from thefinal rules without affecting safety.Accordingly, the FAA has removed thatsentence from the final rules.

Additionally, in order to useterminology in the procedures forexiting the severe icing environmentthat is consistent with the terminologyused in the revised limitation and to

simplify certain language, the FAA hasrevised the first instruction of theprocedures. The revised instructionreads as follows: ‘‘Immediately requestpriority handling from Air TrafficControl to facilitate a route or analtitude change to exit the icingconditions in order to avoid extendedexposure to flight conditions moresevere than those for which the airplanehas been certificated.’’

Comment 44. Request To Change theNote Concerning the Autopilot

One commenter, ATR, requests thatthe FAA revise the second note inparagraph (a)(1) of the proposal forAerospatiale airplanes. As proposed,ATR believes the last sentence of thenote is too restrictive. ATR proposes thefollowing: ‘‘The autopilot may masktactile cues * * * characteristics.Therefore, when any ice is visible on theairplane, the pilot should considerflying manually for short periods inorder to check the absence of anyanomaly.’’

Two commenters request that theFAA remove a similar note concerningthe autopilot from the proposals forairplanes other than Aerospatialemodels. One of the commenters, JAL,states that the note contains advisoryinformation and should not appear inthe Limitations Section of an AFM.

The FAA concurs with ATR’scomment that the last sentence of thenote is too restrictive; that sentence hasbeen removed from the final rules for allairplanes. However, the FAA does notagree with JAL’s contention that theexplanation of the relationship betweenthe autopilot and the masking of tactilecues is inappropriate for insertion in theLimitations Section of an AFM. On thecontrary, the FAA finds that inclusionof such information will increase thelevel of understanding and,consequently, will increase the level ofsafety.

In light of this, the FAA finds that thenote may be removed from paragraph(a)(1) of the final rules for all airplanes;however, the information contained inthe first sentence of that note has beencombined with the autopilot limitationin paragraph (a)(1) of the final rules. Thefinal rules have been revisedaccordingly.

Comment 45. Requests to RemoveAutopilot Limitation

Saab requests that the FAA revise thesecond limitation that appears inparagraph (a)(1) of the proposal for Saabairplanes. As proposed, this limitationindicates that use of the autopilot isprohibited when any ice is observedforming aft of the protected surfaces of


the wing, or when unusual lateral trimrequirements or autopilot trim warningsare encountered. Saab asks that thisautopilot limitation be modified to takeinto consideration the autopilot systemdesign on these airplanes, whichprovides out-of-trim warnings;therefore, the autopilot can be used upto the point where a warning istriggered. Saab adds that the triggeringpoint is early enough for the warning tobe taken, should the reason be ice build-up beyond the protected surfaces.Additionally, there is no automaticdisconnect if the autopilot servo reachesits limit torque, which would preventany surprise to the pilot during an out-of-trim condition.

Another commenter, EMBRAER,requests that use of the autopilot not belimited for EMBRAER Model EMB–120series airplanes. The commenter statesthat flight tests have demonstrated thesafe ability of these airplanes to departa freezing rain/freezing drizzlecondition with the autopilot on.

Raytheon also objects to the autopilotlimitation. Raytheon suggests that abetter approach is to inform the pilotsof the nature of ice accretion, and thenlet the pilots decide when to use theautopilot. The commenter believes thatprohibiting use of the autopilot whenany ice is observed aft of the protectedsurfaces of the wing is a rigidrequirement that takes away a valuableaid to the flight crew when it may beneeded most. Raytheon states that thereis no evidence that the autopilots onBeech aircraft would mask an icingrelated control problem. The commenterpoints out that tests on those aircraftdisclosed no icing related controlproblem to mask. The commenter addsthat trying to anticipate every situationwith an absolute prohibition may leadto other unsafe conditions.

The FAA does not concur that theautopilot limitation should be modifiedor removed from the AD’s for any of theaffected airplanes. The limited amountof time the pilot is using manualcontrols instead of the autopilot wouldnot result in an unsafe condition. Innormal operational environments andconditions, the autopilot is a valuableaid that reduces the workload of theflight crew. However, under abnormalconditions (ice aft of the protectedsurfaces, unusual lateral trim, orautopilot trim warnings), the autopilotwill mask the build-up of large orunusual control forces in one or moreaxes. Therefore, for the short period oftime necessary to exit severe icingconditions, the safest course of actionwould be manual pilot control. Even ifan autopilot does not automaticallydisconnect, the pilot may choose to

disconnect the autopilot and could thenbe faced unexpectedly with unusualcontrol forces. These reasons also stillhold true with airplanes that have beenflight tested with the ice shapes.

Since the issuance of the proposedrules, the FAA has re-examined theautopilot limitation specified inparagraph (a)(1) of the proposals. TheFAA recognizes that clarification isnecessary with regard to its intentconcerning that limitation. Thatlimitation, as specified in the proposals,states that use of the autopilot isprohibited when any ice is observedforming aft of the protected surfaces ofthe wing, or when unusual lateral trimrequirements or autopilot trim warningsare encountered. However, the FAA’sintent concerning that limitation is thatthe autopilot be disconnected when theflight crew observes any of the visualcues identified in paragraph (a)(1) of theAD’s. The need to disconnect theautopilot arises when an amount of iceaccumulates that indicates the limits ofthe ice protection equipment have beenexceeded, regardless of the means bywhich the flight crew becomes aware ofthe accumulation of ice.

Additionally, the FAA acknowledgesthat the autopilot limitation, asproposed, could be misinterpreted tomean that the autopilot must bedisengaged when unusual lateral trim orautopilot trim warnings areencountered, regardless of whether theairplane is in icing conditions.However, the FAA only intended thatthe autopilot limitation apply while theairplane is in icing conditions.

In light of this, the FAA hasdetermined that the autopilot limitationcontained in paragraph (a)(1) of the finalrules must be revised. The FAA haschanged that limitation to read asfollows: ‘‘Since the autopilot may masktactile cues that indicate adversechanges in handling characteristics, useof the autopilot is prohibited when anyof the visual cues specified above exist,or when unusual lateral trimrequirements or autopilot trim warningsare encountered while the airplane is inicing conditions.’’ (This wording isslightly different in the final rule forAerospatiale airplanes because only onevisual cue is provided.) This revisionmore accurately reflects the FAA’sintent and is, therefore, a logicaloutgrowth of the proposed rules.

Comment 46. Request To InsertProcedures in Limitations or AbnormalProcedures Section of AFM

One commenter suggests thatoperations in icing conditions thatexceed the capability of the airplaneshould be described in the Limitations

or Abnormal Procedures Section of theAFM, rather than in the NormalProcedures Section, as specified inparagraph (a)(2) of the proposals.

The FAA concurs partially. The FAAagrees that the Abnormal ProceduresSection may be an appropriate locationfor the procedures for exiting severeicing conditions. However, the FAAdoes not agree that such operationalprocedures should appear in theLimitations Section of the AFM sincesuch procedures are not limitations.Additionally, upon further review, theFAA finds that AFM’s may have neitheran Abnormal Procedures nor a NormalProcedures Section. Consequently, toprovide operators with flexibility as towhere the procedures specified inparagraph (a)(2) should be incorporatedin the AFM, that paragraph has beenrevised to require that the ‘‘Procedures’’Section of the AFM be revised. Thismeans that the procedures may beinserted in the ‘‘Normal Procedures,’’‘‘Abnormal Procedures,’’ or other‘‘Procedures’’ Section of the AFM, asappropriate.

Comment 47. Request To RemoveDuplicate Visual Cues

Two commenters indicate that certainvisual cues specified in paragraph (a)(2)of the proposals are duplicated in the‘‘Warning’’ that is also contained in thatparagraph. One commenter states thatthe duplication of text reduces theimpact of the message. Anothercommenter questions whether the visualcues and procedures for exiting theicing environment are intended to bepart of the AFM material. The FAAinfers from these remarks that thecommenters request that duplicate textbe removed.

Transport Canada Aviation requeststhat the ‘‘Warning’’ be removed becauseindications of the possible hazard areprogressive and may not necessarilyrequire immediate action from the pilot.The commenter suggests that renamingthis as a ‘‘Caution’’ may be moreappropriate.

The FAA concurs partially. The FAAagrees that duplicate text should beremoved from the ‘‘Warning’’ sectionthat appeared in the proposals. TheFAA finds that only one uniqueinstruction appears in the ‘‘Warning’’ inparagraph (a)(2) of the proposals: ‘‘If theflaps are extended, do not retract themuntil the airframe is clear of ice.’’Therefore, the FAA has added thatinstruction to the procedures for exitingthe severe icing environment inparagraph (a)(2) of the AD’s. Theremainder of the ‘‘Warning’’ section thatappeared in the proposals has beenremoved from the final rules.


Comment 48. Request for Revision toInstruction for Flaps Extension

Saab requests that the FAA revise aninstruction contained in the proceduresfor exiting the freezing rain/freezingdrizzle environment in paragraph (a)(2)of the proposals. That instructionindicates to ‘‘Avoid extending flapsduring extended operation in icingconditions * * *.’’ Saab suggests thefollowing: ‘‘Do not extend flaps whenholding in conditions where ice isaccreting on the airframe.’’ Further, thecommenter asks that this instruction beinserted as a ‘‘caution’’ in theLimitations Section of the AFM, ratherthan into the Normal ProceduresSection, as specified in the proposedrule. Saab believes that it is imperativethat the flaps not be extended in suchcases. Inserting the instruction into theLimitations Section, rather than theNormal Procedures Section, would addstrength to the requirement.

Another commenter states that thissame instruction appears to be inconflict with previously approved AFMrevisions which state, ‘‘Sustained flightin icing conditions is prohibited withflaps extended.’’ However, thecommenter does not provide asuggestion for rewording thisinstruction.

The FAA concurs that the proceduresrelated to extension of the flaps can bereworded somewhat. For clarificationpurposes, the FAA has replaced theword ‘‘avoid’’ with ‘‘do not’’ in thatprocedure in paragraph (a)(2) of thefinal rules. This revision eliminates theconflict discussed by the secondcommenter. However, the FAA does notagree that revising the remainder of theinstruction, as suggested by Saab,provides any additional clarification.

The FAA agrees that inserting therevised wording in the LimitationsSection of the AFM, rather than in theNormal Procedures Section, would beacceptable; however, this would expandthe scope of the originally proposedrules and would necessitate reopeningthe comment period to provideadditional opportunity for publiccomment. In light of the time requiredto complete the rulemaking process inadvance of the upcoming icing seasonand in consideration of the safety issuesaddressed by these final rules, the FAAfinds that the AD’s should be issuedwithout additional delay. However, theFAA would consider a request forapproval of an alternative method ofcompliance, in accordance with theprovisions of this AD, to include thisinformation in the Limitations Sectionof an operator’s AFM.

Transport Canada Aviation requeststhat this instruction be revised to readas follows: ‘‘Do not extend flaps duringoperation in icing conditions, except forapproach and landing. Operation withflaps extended will result in a reducedwing angle-of-attack with the possibilityof ice forming on the upper surfacefurther aft on the wing than normal,possibly aft of the protected area.’’

The FAA concurs partially. The FAAdoes not concur with the commenter’ssuggested rewording to limit use of theflaps in all operation in icing conditionsexcept approach and landing. Thewording proposed in the AD’s wouldaffect use of the flaps only duringextended operation in icing conditions.The FAA finds that an amount of icesufficient to cause control problems ismore likely to accumulate duringprolonged operations in icingconditions. Further, the FAA does notconcur that the words ‘‘operation of theflaps can result in a reduced angle-of-attack * * *’’ should be changed to‘‘operation of the flaps will result in areduced angle-of-attack * * *’’ in thisinstruction. Operation with flapsextended does not always result in areduced angle-of-attack. For instance,during extension of the flaps while theairplane is slowing, the angle-of-attackwill increase.

The FAA concurs with the suggestionto include the words ‘‘the possibility ofice forming on the upper surface furtheraft * * * .’’ The FAA acknowledges thatunder certain conditions the dropletswill not impinge further aft with areduced angle-of-attack. The final ruleshave been revised to add the wordssuggested by the commenter to the sixthinstruction specified in the proceduresfor exiting the severe icing environmentcontained in paragraph (a)(2) of theAD’s. That revised instruction reads asfollows: ‘‘Do not extend flaps . . . withthe possibility of ice forming on theupper surface * * * .’’

Comment 49. Requests To Revise‘‘Caution’’ Paragraph

One commenter asks that the heading,‘‘Caution,’’ which appears in paragraph(a)(2) of the proposals, be renamed‘‘Warning’’ because this section isintended to prevent loss of life or injury.Transport Canada Aviation requests thatthe ‘‘Caution’’ section be changed to anote. The commenter provides nojustification.

The FAA concurs partially. The FAAdoes not concur that the ‘‘Caution’’should be changed to a note becausethis section is intended to prevent lossof life or injury. In light of this, the FAAconcurs with the commenter’s request torename the ‘‘Caution’’ section

‘‘Warning.’’ The FAA finds that‘‘Warning’’ is a stronger term and wouldbe a more appropriate heading for theparagraph in question. Additionally, theFAA finds that the ‘‘Warning’’ providesadvisory information that shouldprecede the first limitation in paragraph(a)(1) of the AD’s. Accordingly, the FAAhas revised the heading ‘‘Caution’’ to‘‘Warning’’ in the final rules. Inaddition, the ‘‘Warning’’ has beenplaced at the beginning of paragraph(a)(1) of the final rules. The FAA hasdetermined that including thisinformation in the Limitations Sectionof the AFM will not impose anadditional burden on any operator,since it is informational only and doesnot necessitate providing an additionalopportunity for public comment.

Additionally, the commenter notesthat an undefined term, ‘‘extreme,’’ isused in a sentence in the ‘‘Caution’’paragraph of the proposals, as follows:‘‘Flight in freezing rain, freezing drizzle,or mixed icing conditions (supercooledliquid water and ice crystals) may resultin extreme ice build-up on protectedsurfaces * * * .’’ The FAA infers fromthis remark that the commenter asksthat the word ‘‘extreme’’ be removedfrom the ‘‘Caution’’ paragraph.

The FAA concurs. The FAA finds thatremoving the word ‘‘extreme’’ wouldnot change the intent of the sentenceand may eliminate confusion. The word‘‘extreme’’ has been removed from thissection of the final rule. In addition, forclarification purposes, the FAA hasrevised the first sentence of theproposed ‘‘Caution’’ from ‘‘Severe icingcomprises environmental conditions . ..’’ to ‘‘Severe icing may result fromenvironmental conditions * * * .’’

Comment 50. Request To Remove VisualCues: Identification of Freezing Rain/Freezing Drizzle

One commenter indicates that thecues provided in paragraph (a)(2) of theproposals for identifying freezing rain/freezing drizzle conditions areduplicated in material that appears inparagraph (a)(1) of the proposals. TheFAA infers from this remark that thecommenter requests that duplicativewording be removed from paragraph(a)(2) of the proposed rules.

The FAA concurs. The FAA finds thatthe section entitled ‘‘The following shallbe used to identify freezing rain/freezingdrizzle icing conditions’’ is duplicatedin material that appears in paragraph(a)(1), and does not enhance theeffectiveness of the AD’s. Therefore, thatsection has been removed fromparagraph (a)(2) of the final rules for allairplanes other than Aerospatiale ModelATR–42 and ATR–72 series airplanes.


Paragraph (a)(1) of the proposals forAerospatiale airplanes specifiedsecondary indications for identifyingpossible freezing rain/freezing drizzleconditions. The FAA recognizes that theflight crew could have interpreted thatparagraph to mean that if the secondaryindicators were observed, the airplanemust be flown clear of the severe icingconditions. However, the FAA’s intentis that the flight crew must immediatelyrequest priority handling to exit theicing conditions only when the visualcue (ice on the side window) specifiedin paragraph (a)(1) of the AD isobserved.

Accordingly, the FAA has deleted thesecondary indications of possible severeicing conditions from paragraph (a)(1) ofthe final rule for Aerospatiale airplanes.In addition, the FAA has removed thevisual cue (ice on the side window)from paragraph (a)(2) of the final rule.The FAA has retitled the sectioncontaining the secondary indications ofpossible severe icing as follows: ‘‘Thefollowing may be used as secondaryindications of severe icing conditions.’’Further, the last two secondaryindicators contained in that section arespecified in the final rule in a sectiontitled: ‘‘The following weatherconditions may be conducive to severein-flight icing.’’ (This change isexplained further in Comment 51below.)

Comment 51. Request To Remove VisualCues: Identification of Possible FreezingRain/Freezing Drizzle

One commenter states that the word‘‘may’’ in the following title, whichappears in paragraph (a)(2) of theproposals, is confusing: ‘‘The followingmay be used to identify possiblefreezing rain/freezing drizzleconditions.’’ The commenter indicatesthat AFM procedures should provide aclear sequence of steps that must befollowed and that such proceduresshould be explicit; general advice,regardless of how prudent, should bepublished elsewhere. The FAA infersfrom this remark that the commenterasks that the cues that appear under thissection be deleted.

The FAA does not concur that thissection should be removed. The cuesprovided for identification of possiblesevere icing conditions will alert thepilot to the possibility that unusual iceaccretion may develop. The FAA findsthat the level of detail provided in thefinal rules will increase the level of pilotawareness and, consequently, willincrease the level of safety over thatwhich exists currently. Therefore, theFAA has determined that it is

appropriate to incorporate this sectionin the AFM.

However, the FAA finds thatclarification is necessary with regard tothe title of this section. The FAA findsthat operators may misinterpret thattitle, as proposed, to mean that thissection contains visual cues that shouldbe used to identify possible severe icingconditions prior to takeoff, dispatch, orrelease while the airplane is on theground. Additionally, the FAA findsthat confusion could result indifferentiating between the weatherconditions specified in this section andthe visual cues provided in paragraph(a)(1) of the AD’s. For clarificationpurposes, the FAA has revised the titleof this section to read as follows: ‘‘Thefollowing weather conditions may beconducive to severe in-flight icing.’’

Comment 52. Request To Revise AirTemperature References

Transport Canada Aviation states thatambient temperature is indicated asstatic air temperature (SAT), rather thanoutside air temperature (OAT), for deHavilland Model DHC–8 seriesairplanes. The FAA infers from thisremark the commenter requests that theambient temperature that appears in theweather conditions specified inparagraph (a)(2) of the proposals beexpressed as SAT for those airplanes.

The FAA does not concur. The FAAdoes not intend to specify whichspecific indicator in the cockpit a pilotshould use to determine the ambient airtemperature. The FAA intends that thepilot use whatever means necessary todetermine ambient air temperature.

However, since airplanes may haveindicators other than OAT, the FAA hasreplaced the words ‘‘outside airtemperature’’ with ‘‘ambient airtemperature’’ in the weather conditions,and in the procedures for exiting thesevere icing environment, specified inparagraph (a)(2) of these final rules toeliminate confusion concerning theneed for a specific type of indicator.

In addition, the FAA has re-examinedthe ambient temperature of +5 degreesCelsius that is specified in paragraph(a)(2) of the proposals. The FAA hasdetermined that this temperature is toohigh to be used as a reliable indicationof whether severe icing conditions mayexist during flight. The FAA finds that0 degrees Celsius is a more appropriateindication. The FAA has revisedparagraph (a)(2) of the final rules for allairplanes accordingly.

Comment 53. Request To ReplaceReference to Droplets that Splash orSplatter

JAL requests that the weathercondition that pertains to ‘‘droplets thatsplash or splatter’’ be removed fromparagraph (a)(2) of the proposals. JALbelieves that this weather conditionplaces too much emphasis on subjectivejudgment. JAL states that normal rainconditions will contain droplets thatsplash or splatter upon impact with thewindshield. JAL indicates thatinformation included in its existingAFM revisions, specified as follows,adequately addresses the issue:‘‘Prolonged operation in altitude bandswhere temperatures are near freezingand heavy moisture is visible on thewindscreen should be avoided.’’

The FAA does not concur that thisweather condition should be removedfrom the AD’s. This weather conditionmust be used in conjunction with thetemperature specified as a means ofidentifying severe in-flight icingconditions. The weather condition alsowill alert the pilot to the possibility thatunusual ice accretion may develop. TheFAA finds that the AFM informationsubmitted by JAL does not provide anequivalent alert to the pilot.

Comment 54. Request To ReviseProcedures for Exiting Freezing Rain/Freezing Drizzle

JAL requests that the procedures forexiting freezing rain/freezing drizzlespecified in paragraph (a)(2) of theproposals be restricted to essentialinstructions that the flight crew mustfollow. JAL contends that theprocedures contained in the proposalsare not written in the appropriate formatfor AFM procedures, but are morerepresentative of advisory material. JALalso states that the current FAA-approved AFM procedures for exitingfreezing rain/freezing drizzle alreadyprovide this essential information andconform to the existing style of theAFM’s. Transport Canada Aviationrequests that the first instruction inthese procedures be revised to stateonly: ‘‘Exit the freezing rain or freezingdrizzle conditions immediately.’’ Thecommenter also requests clarification ofthe terms ‘‘extended exposure,’’ as usedin that instruction.

The FAA concurs partially. The FAAhas reviewed the procedures for exitingthe severe icing environment and findsthat two of the instructions contained inthose procedures do not require thelevel of detail provided in the proposedrules. The FAA finds that theinformation concerning masking ofcontrol system forces is already


provided in the Limitations Section ofthe AFM. Therefore, the FAA hasrevised the third instruction of thoseprocedures to read as follows: ‘‘Do notengage the autopilot.’’ Additionally, theFAA has determined that the flight crewneed not be provided with instructionsfor reducing the angle-of-attack becauseinstructions such as this are consideredto be basic airmanship. Accordingly, theFAA has revised the fifth instruction inthe procedures for exiting the severeicing environment to specify onlyinformation that is essential for theflight crew. The revised instructionreads as follows: ‘‘If an unusual rollresponse * * * reduce the angle-of-attack.’’ The FAA finds that, for theremainder of the procedures for exiting,the additional level of details providedin the final rules will increase the levelof understanding and, consequently,will increase the level of safety over thatwhich exists currently. The FAA findsthat these procedures are appropriate forinsertion in the AFM’s.

Regarding the terms ‘‘extendedexposure,’’ the intent of that instructionis to advise the flight crew that exitingthe severe icing conditions willminimize the exposure to flightconditions outside those for which theairplane has been certificated. The FAAfinds that remaining in such conditionsfor a prolonged period may result inaccumulating an amount of icesufficient to cause control problems.The phrase ‘‘to avoid extendedexposure’’ is only intended to explain tothe flight crew why severe icingconditions should be exitedimmediately.

Raytheon questions the necessity totell a commercial pilot not to make anyabrupt or excessive maneuvers if theaircraft is in the position of havingcontrol difficulties. This instructionappears under the heading ‘‘Proceduresfor exiting the freezing rain/freezingdrizzle environment,’’ which appears inparagraph (a)(2) of the proposals. Thecommenter contends that this is atraining issue and is not appropriate forAFM procedures. The FAA infers fromthe commenter’s remark that thecommenter requests that theseinstructions be eliminated from theproposed rules.

The FAA does not concur. The FAAhas determined that such instructionsprovide beneficial guidance to the flightcrew, which will enhance the safety ofthe aircraft.

Saab requests that the FAA revise oneof the instructions specified in theprocedures for exiting freezing rain/freezing drizzle specified in theproposals. The instruction states that ifan unusual roll response or

uncommanded control movement isobserved, the angle-of-attack should bereduced by increasing the airspeed orrolling the wings level (if in a turn), andapplying additional power, if needed.Saab suggests that this instruction berevised to include the word ‘‘aileron’’ inthe reference to uncommanded controlmovement. Saab states further that inthe case of wing ice beyond theprotected surfaces, the application ofpower may be appropriate to increaseairspeed/improve airflow. However, ifice has accrued on the wings beyond theprotected surfaces, there is a possibilitythat there also is ice on the horizontalstabilizers. In this case, a sudden burstof power may be detrimental. Anuncommanded pitch control movementis indicative of tail ice, which normallycalls for a different action, bothconcerning power as well as thehandling of flaps, if extended. Anothercommenter, Transport Canada Aviation,requests that the same instruction berevised to include the word ‘‘lateral’’ inreference to ‘‘uncommanded controlmovement,’’ and to change the phrase‘‘or rolling wings level’’ to ‘‘and rollingwings level.’’

The FAA concurs partially. The FAAagrees that the correct procedures forreducing the angle-of-attack is toincrease the airspeed and roll the wingslevel, if in a turn. However, as explainedpreviously, this portion of the procedurehas been removed from the final rules.The FAA does not agree that either‘‘lateral’’ or ‘‘aileron’’ should be used tospecify the type of uncommandedcontrol movement. The FAA finds thatuse of the term ‘‘lateral’’ may not beunderstood by the flight crew. The FAAfinds that including the word ‘‘aileron’’may clarify which control surface is ofconcern; however, the FAA hasdetermined that use of a more generalterm, ‘‘roll’’ will correctly specify thetype of uncommanded controlmovement that is of concern. The FAAhas revised the fifth instruction in theprocedures for exiting the severe icingenvironment in paragraph (a)(2) of thefinal rules accordingly. The revisedinstruction reads as follows: ‘‘If anunusual roll response or uncommandedroll control movement is observed,reduce the angle-of-attack.’’

In addition, the procedures for exitingthe freezing rain/freezing drizzleenvironment contained in the proposalsdid not specify to use ‘‘a sudden burstof power’’ when reducing the angle-of-attack. Rather, the proposed procedureindicates to apply additional power, ifneeded, to provide the desired flightpath. However, as discussed previously,the FAA has removed this referencefrom the final rules. In addition, as

explained previously, the FAA hasrevised the final rules to add the word‘‘roll’’ to describe the type ofuncommanded control movement. Thisrevised wording addresses Saab’sconcern regarding increasing power fora pitch anomaly.

Saab also notes that this instructionrecommends a reduction in the angle-of-attack and application of power, ifneeded. However, the next instructionof the procedures indicates thatreducing the angle-of-attack may causeice to build up beyond the protectedareas of the wing. Saab concludes thatthere is a conflict in that the proposedAD would require that the angle-of-attack not be reduced or ice will collectbeyond the protected surfaces; however,the angle-of-attack must be reduced ifthere is an unusual roll response oruncommanded control movement.

The FAA does not concur with thecommenter’s contention that there is aconflict in the AD’s. Reducing the angle-of-attack by increasing airspeed orrolling the wings level (if in a turn), andapplying additional power, if needed, isa procedure used to exit severe icingconditions following an unusual rollresponse or uncommanded roll controlmovement; whereas the instruction thatinvolves not extending the flaps duringextended operation in icing conditionsis intended to prevent ice build-upbeyond the unprotected surfaces.

Raytheon asks for removal of theinstruction to reduce the angle-of-attackand apply additional power, if needed,in response to an unusual roll responseor uncommanded control movement.The commenter states that these arenormal instructions with respect towing stall and are inappropriate forinclusion in an AFM.

The FAA concurs partially. Theremay not be a stall warning associatedwith uncommanded control movementsin the case of encounters with severeicing conditions. Since this is not a‘‘normal’’ stall, the flight crew may notrecognize that normal stall recoveryprocedures should be used. However, asstated previously, the instructionreferenced by the commenter has beendeleted, in part, from the final rules.

Raytheon also states that it is notappropriate to require contact with AirTraffic Control as part of an AFMprocedure since this is alreadyaddressed in the AeronauticalInformation Manual and in section91.183 of the Federal AviationRegulations (14 CFR 91.183). The FAAinfers from this statement that thecommenter requests that the instructionto contact Air Traffic Control should beremoved from the procedures for exitingsevere icing conditions.


The FAA does not concur. The FAAis aware that this instruction iscontained in the references provided bythe commenter. However, the FAA findsthat the importance of timelydissemination of this instructionwarrants its inclusion in the final rules.Inclusion of instructions of this type isnot without precedent; for example,similar information also is specified incertain AFM’s where the forward lookwindshear system is addressed.

Comment 55. Request To ReviseProcedures for Exiting the Severe IcingEnvironment: Include Airplane-SpecificInstructions

One commenter suggests that anyaction that might be necessary tooptimize aircraft performance andcontrol in conditions of exceptionalicing, and exit from those conditions,should be determined separately witheach manufacturer; such proceduresshould be contained in the AFM foreach airplane model. The FAA infersfrom this remark that the commenterrequests that the FAA revise theprocedures for exiting the severe icingenvironment in each final rule toinclude airplane-specific instructions.

The FAA agrees that proceduresobtained from each individualmanufacturer should be considered andincluded in the final rules, ifappropriate. All manufacturers havebeen provided with an opportunity tosubmit such procedures in response tothe proposed rules. Some manufacturersrequested changes to the final rules. TheFAA has revised the final rules for thoserequests that were substantiatedadequately. Following issuance of thefinal rules, the FAA would consider arequest to include additional changes tothe AFM revisions, in accordance withthe provisions of these AD’s, providedthat adequate justification is presentedto support such a request.

Comment 56. Revision of Procedures forExiting the Severe Icing Environment

The FAA has re-examined the sectiontitled ‘‘Procedures for exiting the severeicing environment’’ in paragraph (a)(2)of the proposals. As proposed, thatsection states that if the visual cues usedfor identifying ‘‘possible’’ freezing rainor freezing drizzle conditions areobserved, the flight crew should followthe procedures specified for exitingthose conditions. The FAA did notintend that the flight crew use theprocedures for exiting the severe icingenvironment when the weatherconditions specified in paragraph (a)(2)of these AD’s are observed. The FAA’sintent is that the flight crew use thoseprocedures only when the visual cues

identified in the Limitations Section ofthe AFM are observed.

In order to eliminate any confusion,the FAA has revised the last sentence ofthe first paragraph in the procedures forexiting the severe icing environment.The FAA has removed the word‘‘possible’’ from that sentence, and hasadded clarification that the visual cuesare specified in the Limitations Sectionof the AFM. The revised sentence readsas follows: ‘‘If the visual cues specifiedin the Limitations Section of the AFMfor identifying severe icing conditionsare observed, accomplish thefollowing.’’ (Operators should note that,for Aerospatiale airplanes, the final rulespecifies only one visual cue, whichinvolves ice on the side window.)

Comment 57. Request To Revise CostEstimate

Transport Canada requests that theFAA provide an operational costestimate in the proposed AD’s.

The FAA acknowledges the concernof the commenter. The FAA recognizesthat, in accomplishing the requirementsof any AD, operators may incur othercosts in addition to the ‘‘direct’’ coststhat are reflected in the cost analysispresented in the AD preamble.However, the cost analysis in ADrulemaking actions typically onlyincludes such direct costs. In the case ofthese AD’s, for example, therequirements are to revise the AFM toinclude certain information. Howoperators actually ‘‘implement’’ thatinformation thereafter (once it is placedin the AFM) may vary greatly amongthem.

Further, because AD’s require specificactions to address specific unsafeconditions, they appear to impose coststhat would not otherwise be borne byoperators. However, because of thegeneral obligation of operators tomaintain and operate aircraft in anairworthy condition, this appearance isdeceptive. Attributing those costs solelyto the issuance of this AD is unrealisticbecause, in the interest of maintainingand operating safe aircraft, prudentoperators would accomplish therequired actions even if they were notrequired to do so by the AD. In any case,the FAA has determined that direct andincidental costs are still outweighed bythe safety benefits of the AD.

The FAA points out that it is notrequired to do a full cost-benefitanalysis for each AD. AD’s wereexplicitly exempted from the Office ofManagement and Budget (OMB)coordination process described inSection 6 of that Executive Order. As amatter of law, in order to be airworthy,an aircraft must conform to its type

design and be in a condition for safeoperation. The type design is approvedonly after the FAA makes adetermination that it complies with allapplicable airworthiness requirements.In adopting and maintaining thoserequirements, the FAA has alreadymade the determination that theyestablish a level of safety that is cost-beneficial. When the FAA later makes afinding of an unsafe condition in anaircraft and issues an AD, it means thatthe original cost beneficial level ofsafety is no longer being achieved andthat the required actions are necessaryto restore that level of safety. Becausethis level of safety has already beendetermined to be cost beneficial, andbecause the AD does not add anadditional regulatory requirement thatincreases the level of safety beyondwhat has been established by the typedesign, a full cost-benefit analysis foreach AD would be redundant andunnecessary.

Comment 58. Requests To DelayIssuance of the Final Rules

Three commenters request that theFAA extend the comment period for theproposed rules by 90 days. Each of thecommenters request the extension inorder to complete a comprehensiveanalysis of this issue. The commentersstate their involvement in focusing on‘‘* * * other recent rulemaking activity,including the Commuter Rule, flightcrewmember training requirements, andproposed rules covering flight crewflight, duty and test requirements* * *’’ as a reason that did not allowcomplete analysis of the proposed AD’s.

One commenter requests thatimplementation of the AD’s be deferreduntil further discussion with industryhas been undertaken.

The FAA has reviewed these requestsand, in consideration of the importanceand need for dissemination of thisimportant information to the aviationcommunity, does not concur that thecomment period should be extended orissuance of the final rules be deferreduntil a later date. Issuing the final ruleswill ensure that the information isavailable, understood, and implementedby the aviation community before thenext icing season. For these reasons, theFAA has determined that it isimperative that the information andactions contained in these final rules beincorporated into the operators’ AFM’simmediately.

ConclusionAfter careful review of the available

data, including the comments notedabove, the FAA has determined that airsafety and the public interest require the


adoption of the rule with the changespreviously described. The FAA hasdetermined that these changes willneither increase the economic burdenon any operator nor increase the scopeof the AD.

Cost Impact

The FAA estimates that 158Aerospatiale Model ATR–42 and ATR–72 series airplanes of U.S. registry willbe affected by this AD, that it will takeapproximately 1 work hour per airplaneto accomplish the required actions, andthat the average labor rate is $60 perwork hour. Based on these figures, thecost impact of the AD on U.S. operatorsis estimated to be $9,480, or $60 perairplane.

For Model ATR–42 series airplanes,Modification 4216 (or 4222), as requiredin this AD, will take approximately 52work hours per airplane to accomplish,at an average labor rate of $60 per workhour. Required parts will be supplied bythe manufacturer at no cost to operators.Based on these figures, the cost impacton U.S. operators for this modificationis estimated to be $492,960, or $3,120per airplane.

For Model ATR–72 series airplanes,Modification 4215 (or 4221), as requiredin this AD, will take approximately 96work hours per airplane to accomplish.Required parts for this modification willbe supplied by the manufacturer at nocost to operators. Modification 4213, asrequired in this AD, would takeapproximately 4 work hours toaccomplish. Required parts will costapproximately $200 per airplane. Theaverage labor rate for accomplishment ofboth modifications is $60 per workhour. Based on these figures, the costimpact on U.S. operators for thesemodifications is estimated to be$979,600, or $6,200 per airplane.

The cost impact figures discussedabove are based on assumptions that nooperator has yet accomplished any ofthe requirements of this AD action, andthat no operator would accomplishthose actions in the future if this ADwere not adopted.

In addition, the FAA recognizes thatthis AD may impose operational costs.However, those costs are incalculablebecause the frequency of occurrence ofthe specified conditions and theassociated additional flight time areindeterminable. Nevertheless, becauseof the severity of the unsafe conditionaddressed, the FAA has determined thatcontinued operational safetynecessitates the imposition of thesecosts.

Regulatory Impact

The regulations adopted herein willnot have substantial direct effects on theStates, on the relationship between thenational government and the States, oron the distribution of power andresponsibilities among the variouslevels of government. Therefore, inaccordance with Executive Order 12612,it is determined that this final rule doesnot have sufficient federalismimplications to warrant the preparationof a Federalism Assessment.

For the reasons discussed above, Icertify that this action (1) is not a‘‘significant regulatory action’’ underExecutive Order 12866; (2) is not a‘‘significant rule’’ under DOTRegulatory Policies and Procedures (44FR 11034, February 26, 1979); and (3)will not have a significant economicimpact, positive or negative, on asubstantial number of small entitiesunder the criteria of the RegulatoryFlexibility Act. A final evaluation hasbeen prepared for this action and it iscontained in the Rules Docket. A copyof it may be obtained from the RulesDocket at the location provided underthe caption ADDRESSES.

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviationsafety, Incorporation by reference,Safety.

Adoption of the Amendment

Accordingly, pursuant to theauthority delegated to me by theAdministrator, the Federal AviationAdministration amends part 39 of theFederal Aviation Regulations (14 CFRpart 39) as follows:

PART 39—AIRWORTHINESSDIRECTIVES

1. The authority citation for part 39continues to read as follows:

Authority: 49 USC 106(g), 40113, 44701.

§ 39.13 [Amended]2. Section 39.13 is amended by

removing amendment 39–9152 (60 FR9616, February 21, 1995), and by addinga new airworthiness directive (AD),amendment 39–9604, to read as follows:96–09–28 Aerospatiale: Amendment 39–

9604. Docket 95–NM–146–AD.Supersedes AD 95–02–51, Amendment39–9152.

Applicability: All Model ATR–42 andATR–72 series airplanes, certificated in anycategory.

Note 1: This AD applies to each airplaneidentified in the preceding applicabilityprovision, regardless of whether it has beenotherwise modified, altered, or repaired inthe area subject to the requirements of this

AD. For airplanes that have been modified,altered, or repaired so that the performanceof the requirements of this AD is affected, theowner/operator must request approval for analternative method of compliance inaccordance with paragraph (d) of this AD.The request should include an assessment ofthe effect of the modification, alteration, orrepair on the unsafe condition addressed bythis AD; and, if the unsafe condition has notbeen eliminated, the request should includespecific proposed actions to address it.

Compliance: Required as indicated, unlessaccomplished previously.

To minimize the potential hazardsassociated with operating the airplane insevere icing conditions by providing moreclearly defined procedures and limitationsassociated with such conditions, accomplishthe following:

(a) Within 30 days after the effective dateof this AD, accomplish the requirements ofparagraphs (a)(1) and (a)(2) of this AD.

Note 2: Operators must initiate action tonotify and ensure that flight crewmembersare apprised of this change.

(1) Revise the FAA-approved AirplaneFlight Manual (AFM) by incorporating thefollowing into the Limitations Section of theAFM. This may be accomplished by insertinga copy of this AD in the AFM.

‘‘WARNINGSevere icing may result from

environmental conditions outside of those forwhich the airplane is certificated. Flight infreezing rain, freezing drizzle, or mixed icingconditions (supercooled liquid water and icecrystals) may result in ice build-up onprotected surfaces exceeding the capability ofthe ice protection system, or may result in iceforming aft of the protected surfaces. This icemay not be shed using the ice protectionsystems, and may seriously degrade theperformance and controllability of theairplane.

• During flight, severe icing conditionsthat exceed those for which the airplane iscertificated shall be determined by thefollowing visual cue. If the following visualcue exists, immediately request priorityhandling from Air Traffic Control to facilitatea route or an altitude change to exit the icingconditions.—Severe icing is characterized by ice

covering all or a substantial part of theunheated portion of either forward sidewindow, possibly associated with watersplashing and streaming on thewindshield.• Since the autopilot may mask tactile

cues that indicate adverse changes inhandling characteristics, use of the autopilotis prohibited when the visual cue specifiedabove exists, or when unusual lateral trimrequirements or autopilot trim warnings areencountered while the airplane is in icingconditions.

• All icing detection lights must beoperative prior to flight into icing conditionsat night. [NOTE: This supersedes any reliefprovided by the Master Minimum EquipmentList (MMEL).]’’

• The ice detector must be operative forflight into icing conditions.


(2) Revise the FAA-approved AFM byincorporating the following into theProcedures Section of the AFM. This may beaccomplished by inserting a copy of this ADin the AFM.

‘‘THE FOLLOWING MAY BE USED ASSECONDARY INDICATIONS OF SEVEREICING CONDITIONS:

• Unusually extensive ice accreted on theairframe in areas not normally observed tocollect ice.

• Accumulation of ice on the lower surfaceof the wing aft of the protected area.

• Accumulation of ice on the propellerspinner farther aft than normally observed.

THE FOLLOWING WEATHER CONDITIONSMAY BE CONDUCIVE TO SEVERE IN-FLIGHT ICING:

• Visible rain at temperatures below 0degrees Celsius ambient air temperature.

• Droplets that splash or splatter on impactat temperatures below 0 degrees Celsiusambient air temperature.

PROCEDURES FOR EXITING THE SEVEREICING ENVIRONMENT:

These procedures are applicable to allflight phases from takeoff to landing. Monitorthe ambient air temperature. While severeicing may form at temperatures as cold as¥18 degrees Celsius, increased vigilance iswarranted at temperatures around freezingwith visible moisture present. If the visualcue specified in the Limitations Section ofthe AFM for identifying severe icingconditions is observed, accomplish thefollowing:

• Immediately request priority handlingfrom Air Traffic Control to facilitate a routeor an altitude change to exit the severe icingconditions in order to avoid extendedexposure to flight conditions more severe

than those for which the airplane has beencertificated.

• Avoid abrupt and excessivemaneuvering that may exacerbate controldifficulties.

• Do not engage the autopilot.• If the autopilot is engaged, hold the

control wheel firmly and disengage theautopilot.

• If an unusual roll response oruncommanded roll control movement isobserved, reduce the angle-of-attack.

• Do not extend flaps during extendedoperation in icing conditions. Operation withflaps extended can result in a reduced wingangle-of-attack, with the possibility of iceforming on the upper surface further aft onthe wing than normal, possibly aft of theprotected area.

• If the flaps are extended, do not retractthem until the airframe is clear of ice.

• Report these weather conditions to AirTraffic Control.’’

(b) Within 6 months after the effective dateof this AD, modify the deicing boots on theleading edges of the wing by accomplishingeither paragraph (b)(1) or (b)(2) of this AD, asapplicable.

(1) For Model ATR–42 series airplanes:Accomplish Aerospatiale Modification 4216(during retrofit) or 4222 (during production),as applicable. Modification 4216 shall beaccomplished in accordance withAerospatiale Service Bulletin ATR42–30–0059, Revision 1, dated April 10, 1995; andATR42–57–0043, Revision 1, dated April 10,1995. Modification 4222 shall beaccomplished in accordance withAerospatiale Service Bulletin ATR42–57–0043, Revision 1, dated April 10, 1995.

(2) For Model ATR–72 series airplanes:Accomplish Aerospatiale Modification 4215(during retrofit) or 4221 (during production),as applicable. Modification 4215 shall beaccomplished in accordance with

Aerospatiale Service Bulletin ATR72–30–1023, Revision 1, dated April 10, 1995;ATR72–57–1015, Revision 1, dated April 10,1995; and ATR72–57–1016, Revision 1, datedApril 10, 1995. Modification 4221 shall beaccomplished in accordance withAerospatiale Service Bulletin ATR72–57–1015, Revision 1, dated April 10, 1995; andATR72–57–1016, Revision 1, dated April 10,1995.

(c) For Model ATR–72 series airplanes:Within 6 months after the effective date ofthis AD, install Aerospatiale Modification4213, ‘‘Flaps Extension Inhibition above VFE15 deg.,’’ in accordance with AerospatialeService Bulletin ATR72–27–1039, datedJanuary 12, 1995.

(d) An alternative method of compliance oradjustment of the compliance time thatprovides an acceptable level of safety may beused if approved by the Manager,Standardization Branch, ANM–113, FAA,Transport Airplane Directorate. Operatorsshall submit their requests through anappropriate FAA Principal OperationsInspector, who may add comments and thensend it to the Manager, StandardizationBranch, ANM–113.

Note 3: Information concerning theexistence of approved alternative methods ofcompliance with this AD, if any, may beobtained from the Standardization Branch,ANM–113.

(e) Special flight permits may be issued inaccordance with sections 21.197 and 21.199of the Federal Aviation Regulations (14 CFR21.197 and 21.199) to operate the airplane toa location where the requirements of this ADcan be accomplished.

(f) The modifications shall be done inaccordance with the following Aerospatialeservice bulletins, which contain the specifiedeffective pages:

Service bulletin referenced and date Page No. Revision levelshown on page Date shown on page

ATR42–30–0059, Revision 1, April 10, 1995 ............................................. 1–3, 12–17, 31, 32 1 April 10, 1995.4–11, 18–30, 33–36 Original March 20, 1995.

ATR42–57–0043, Revision 1, April 10, 1995 ............................................. 1–4, 6, 8 1 April 10, 1995.5, 7, 9–18 Original March 20, 1995.

ATR72–30–1023, Revision 1, April 10, 1995 ............................................. 1, 2, 12–17, 33, 34 1 April 10, 1995.3–11, 18–32, 35–38 Original March 20, 1995.

ATR72–57–1015, Revision 1, April 10, 1995 ............................................. 1, 2, 5, 6, 8, 11, 15 1 April 10, 1995.3, 4, 7, 9, 10, 12–14, 16 Original March 20, 1995.

ATR72–57–1016, Revision 1, April 10, 1995 ............................................. 1, 2, 5, 6, 8, 11, 15 1 April 10, 1995.3, 4, 7, 9, 10, 12–14 Original March 20, 1995.

The incorporation by reference of thesedocuments was approved by the Director ofthe Federal Register in accordance with 5U.S.C. 552(a) and 1 CFR part 51. Theinstallation shall be done in accordance withAerospatiale Service Bulletin ATR72–27–1039, dated January 12, 1995. Theincorporation by reference of thesedocuments was approved previously by theDirector of the Federal Register, inaccordance with 5 U.S.C. 552(a) and 1 CFRpart 51, as of March 8, 1995 (60 FR 9616,February 21, 1995). Copies may be obtainedfrom Aerospatiale, 316 Route de Bayonne,31060 Toulouse, Cedex 03, France. Copies

may be inspected at the FAA, TransportAirplane Directorate, 1601 Lind Avenue,SW., Renton, Washington; or at the Office ofthe Federal Register, 800 North CapitolStreet, NW., suite 700, Washington, DC.

(g) This amendment becomes effective onJune 11, 1996.

Issued in Renton, Washington, on April 24,1996.Ronald T. Wojnar,Manager, Transport Airplane Directorate,Aircraft Certification Service.

Certified to be a true copy of the original.Lori Aliment,Certifying Officer.[FR Doc. 96–10744 Filed 5–1–96; 3:25 pm]BILLING CODE 4910–13–P

Documents

20646 Federal Register /Vol. 61, No. 89/Tuesday, May 7