Fatigue Evaluation Indicates Most Aviation Maintenance ... · Fatigue Evaluation Indicates Most Aviation Maintenance Personnel Obtain Insufficient Sleep An FAA evaluation of the effects

NOVEMBER–DECEMBER 2001

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Aviation Mechanics Bulletin

Fatigue EvaluationIndicates Most Aviation

Maintenance Personnel ObtainInsufficient Sleep

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Fatique Evaluation Indicates Most Aviation MaintenancePersonnel Obtain Insufficient Sleep ..............................................................1

Maintenance Alerts ..................................................................................... 11

News & Tips ............................................................................................... 17

November–December 2001 Vol. 49 No. 6

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Fatigue EvaluationIndicates Most AviationMaintenance Personnel

Obtain Insufficient Sleep

An FAA evaluation of the effects of fatigue and workplaceenvironmental factors on 500 maintenance personnel

revealed that most slept less than the 7.5–8 hours a dayrecommended by specialists and that 50 percent sometimes

felt tired at work. Thirty percent said that fatigue had anegative effect on their work performance.

FSF Editorial Staff

Because aviation maintenance per-sonnel often work in conditions thatcan contribute to fatigue, researchersevaluated workplace environmentalconditions and the amount of sleepobtained by aviation maintenancepersonnel.

The evaluation is part of the U.S. Fed-eral Aviation Administration (FAA)

Human Factors Issues in AircraftMaintenance and Inspection Re-search Program and part of a com-prehensive ongoing research programto determine the effects of fatigue andworkplace conditions on workplaceerrors.

The evaluation was designed to col-lect “a large amount of diverse data.”

2 FLIGHT SAFETY FOUNDATION • AVIATION MECHANICS BULLETIN • NOVEMBER–DECEMBER 2001

One phase of the project involvedcollection of “hot-weather data” frommaintenance personnel who workedfor U.S. airlines in the southeasternUnited States and the southwesternUnited States during the warmestmonths of the year — July throughSeptember, said the report on theevaluation.

Hot-weather data were collected fromtwo groups:

• One hundred aviation mainte-nance personnel whose jobswere “in the environment, in-cluding line maintenance … andheavy maintenance in largehangars,” the report said. (Datawere not collected from mainte-nance personnel who workedin small-component repairshops or climate-controlled re-pair shops.) The personnel whoparticipated in this phase of thedata collection worked for threelarge air carriers. They wore twotypes of equipment — one tomonitor the temperature, lightingand sound levels in their workenvironments and the second tomonitor the duration of theirsleep — for two weeks; and,

• The same 100 personnel and 399other aviation maintenance per-sonnel who worked in the threeair carriers’ maintenance organi-zations and who volunteered to

respond to a 41-question surveyabout fatigue and work condi-tions. The report said that thesurvey was intended to help re-searchers understand “selecteddata associated with personallife, [such as] exercise, eating,sleeping, perceived job satisfac-tion and other such factors.”

Most aviation maintenancepersonnel are men, and more than97 percent of the participants in theevaluation were men. Ages of the par-ticipants ranged from 25 years to65 years; the average age was 39years. Most participants were linepersonnel and hangar personnel. (Theresearchers had discouraged partici-pation by maintenance personnelwhose work was primarily supervi-sory or managerial.)

Monitoring EquipmentShows Daily SleepPeriods Averaged

Five Hours

The sleep evaluation determinedperiods of the participants’ actualsleep and “assumed sleep.” Actualsleep was calculated by software in awatchlike device worn on the wristthat measured each wearer’s activityand plotted the activity levels on achart; assumed sleep was derived byresearchers who examined each chartto determine when inactivity began

FLIGHT SAFETY FOUNDATION • AVIATION MECHANICS BULLETIN • NOVEMBER–DECEMBER 2001 3

(when the wearer went to bed) andwhen activity resumed (when thewearer arose). The period of assumedsleep typically was about 50 minuteslonger than the period of actual sleep.

Evaluation of the sleep data showedthat the average daily sleep period forthe 100 participating maintenancepersonnel was about five hours.

A different device — about the size ofa pack of cigarettes and worn in thefront pocket during work hours — col-lected data on temperatures, sound lev-els and light levels. The device recordedan average reading every two minutes.Results included the following:

• The average workplace tempera-ture was 86 degrees Fahrenheit([F]; 30 degrees Celsius [C]) inlarge hangars and 84 degrees F(29 degrees C) for line main-tenance. (Humidity levels werenot included in calculations oftemperature.) Average temper-atures during the day shift(typically beginning around day-break) were 87 degrees F (31 de-grees C); during the afternoonshift (typically beginning at mid-afternoon), temperatures aver-aged 86 degrees F; and during thenight shift (typically beginningabout midnight), temperaturesaveraged 84 degrees F. The high-est temperature recorded duringthe study was 130 degrees F

(54 degrees C). The report saidthat the 130-degree temperaturewas “not surprising” because theU.S. National Weather Servicehad reported outdoor tempera-tures in the area of more than 110degrees F (43 degrees C);

• The average sound level was 67.7decibels. [A decibel is a measure-ment of loudness. Each decibel isequal approximately to the small-est degree of difference of loud-ness ordinarily detectable by thehuman ear, the range of which in-cludes about 130 decibels on ascale beginning with 1 decibel forthe faintest audible sound.1 TheU.S. National Institute of Occu-pational Safety and Health hassaid that normal conversation ismeasured at about 60 decibels; ajet engine during takeoff measuresabout 140 decibels. People whoare exposed — without hearingprotection — to noises louder thanabout 85 decibels for long periodsof time may experience perma-nent hearing loss.2] Noise levelsexperienced by maintenance linepersonnel and personnel workingin large hangars were similar.The average sound level on thenight shift was lower than at oth-er times — 59 decibels; for the dayshift, the average sound level was67.7 decibels, and for the after-noon shift, the average soundlevel was 73.2 decibels; and,


• Light levels were measured inlumens per square meter.3 [A lu-men is a measurement of lightenergy in the air. For example, a60-watt incandescent light bulbprovides about 850 lumens oflight.4] Light levels ranged froman average of 172 lumens persquare meter on the night shiftto an average of 1,182 lumensper square meter on the after-noon shift; the overall light mea-surement was an average of 692lumens per square meter. Theaverage light measurement formaintenance personnel workingin large hangars was 578 lumensper square meter; the average forline maintenance personnel was979 lumens per square meter.

Survey ResponsesConflict With

Sleep Data FromMonitoring Equipment

The 499 respondents to the 41-question survey comprised main-tenance personnel at four airports inthe southern United States.

Forty-six percent of the maintenancepersonnel responding to the surveyworked in airframe maintenance;the remainder worked in 10 othermaintenance-area categories, includ-ing avionics, machine shop, compo-nent, power plant, structure/bond,

modification line, interiors, qualityassurance/inspection and apprentice.

Nearly 42 percent of respondentswere from age 36 to age 45, about 30percent of respondents were from age26 to age 35, and about 20 percent ofrespondents were from age 46 to age55. Less than 10 percent of respon-dents were from age 56 to age 65, lessthan 3 percent of respondents wereage 25 years or younger, and less than1 percent were age 66 years or older.

Nearly 90 percent of all respondentshad more than five years experiencein aviation maintenance, includingnearly 38 percent with from 10 yearsto 14 years of experience, about 20percent with from 15 years to 19 yearsof experience and about 20 percentwith 20 years or more of experience.

Most respondents (43 percent) workedthe day shift at the time of the survey.About 30 percent worked the nightshift, and about 25 percent worked theafternoon shift.

Survey questions about sleep,fatigue and alertness on the job yield-ed the following responses:

• More than 50 percent of the re-spondents said that they felt mostalert at the beginning of theirwork shifts;

• More than 50 percent of respon-dents said that they “sometimes”


felt fatigued at work, but onlyabout 30 percent of respondentssaid that fatigue had a negativeeffect on their job performance;

• More than 30 percent of respon-dents said that they had sleptbetween six hours and sevenhours the night before they an-swered the survey questions;about 25 percent said that theyhad slept between five hours andsix hours; about 20 percent saidthat they had slept betweenseven hours and eight hours;about 15 percent said that theyhad slept less than five hours;and less than 10 percent saidthat they had slept more thaneight hours. The report said thatresponses to this question appar-ently were “unaligned with theactual sleep data collected” withmonitoring equipment.

“[The response to the question]shows that over 60 percent ofthe respondents reported thatthey [had] slept over six hoursthe previous night,” the reportsaid. “However, the [monitoringequipment] data show accurate-ly that the average sleep wasabout five hours. The [monitor-ing equipment] data also indicatethat about 67 percent of the [re-spondents] slept, on average, be-tween 4.2 [hours] and six hours.This difference in data … maybe attributable to numerous

factors. First, the respondentsmay be over-reporting their sleepslightly. Secondly, the [monitor-ing equipment] is very accurateand does not count the initial‘tossing and turning’ as sleep.Thus, there is a likely differencebetween the time in bed vs. theactual sleep time.”

The difference between the datagathered by the monitoringequipment and the data collect-ed by the survey and an earlierfatigue survey5 “strongly sug-gests that maintenance personnelare not fully aware of their sleepduration and the possible fatiguethat may result,” the report said;and,

• Most respondents said that theydid not observe changes in theiralertness from the beginning ofa work shift to the end of a workshift.

“The collective set of these data andfigures suggests that the airlinemaintenance workers do not perceivefatigue as a major problem,” the re-port said.

Nevertheless, the responses indicat-ed differences between the shiftworked and the perception of fatigue,the report said. Day-shift respondents“may take a little longer to ‘wakeup’ than the afternoon-[shift] andevening-shift [respondents],” the


report said. About 45 percent ofday-shift respondents said thatthey felt alert at the beginning of ashift, compared with about 60 percentof afternoon-shift respondents andnight-shift respondents.

A higher percentage of night-shiftrespondents (35 percent) said thatthey are “frequently,” “very frequent-ly” or “always” fatigued at work,compared with day-shift respondents(23.9 percent) and afternoon-shiftrespondents (16.6 percent).

“[These] data suggest that shift workis related to fatigue, such that night-shift [respondents] are more likely toreport being fatigued on the job,” thereport said.

Almost 30 percent of respondentssaid that fatigue had a negative effecton their job performance, includingmore than 40 percent of night-shift respondents, 25 percent of day-shift respondents and 19 percent ofafternoon-shift respondents.

“Night-shift [respondents] have a dif-ferent perspective about fatigue in com-parison to the day[-shift respondents]and afternoon-shift [respondents],” thereport said. “This indicates that fatigueis perceived to be more of a problemby night-shift [respondents].”

When asked to assess their level ofalertness throughout their work shifts,

day-shift respondents and afternoon-shift respondents said that their alert-ness levels were about the same.Night-shift respondents, however,said that their alertness levels de-creased from the beginning of theshift to the end of the shift.

The responses provided “more evi-dence that [respondent] perceptionsof alertness vary as a function of theshift worked by the [respondent],” thereport said.

“While other factors, such as envi-ronmental factors, may have an im-pact on fatigue and alertness, thesedata present evidence that workingthe night shift is linked with higherlevels of fatigue, lower levels of alert-ness and reduced levels of perceivedjob performance.”

Survey questions about workplaceenvironment resulted in the follow-ing responses:

• More respondents said thatthey were bothered more by hightemperatures than by problemswith sound levels or light levels.Sixty-nine percent of respon-dents said that heat affectedtheir job performance. Ninety-seven percent of respondentssaid that water was readily acces-sible while they worked; 80 per-cent said that they drank waterat least three times a day, and 39


percent said that they drank atleast five glasses of water a day;

• Forty-five percent of respon-dents said that they “frequent-ly” worked in inadequatelylighted facilities, and more than40 percent of respondents saidthat inadequate lighting had anegative effect on their job per-formance. (The phrasing of thesurvey question did not elicitinformation about the specificways in which inadequate light-ing affected performance); and,

• Fifty-eight percent of respondentssaid that “noise” had a negativeeffect on their job performance.

Report RecommendsEducation on

Importance of Sleep

Most sleep researchers recommendthat people sleep between 7 1/2 hoursand eight hours a day,6 and nonewould consider adequate the approx-imately five hours of sleep (or the sixhours of “assumed sleep”) achievedby aviation maintenance personnel,the report said.

“The sleep experts would argue thatthe population of maintenance per-sonnel is acquiring a daily ‘sleep debt’of at least two hours,” the report said.“Since the [monitoring equipment]was worn seven days a week for the

two-week data-collection period, itdoes not appear that maintenancepersonnel are repaying the sleep debt.… [T]he questionnaire data … doesnot reflect a population that perceiveschronic fatigue or tiredness. The datacollected from the [monitoring equip-ment] strongly suggest that thepopulation of aviation maintenanceworkers has a sleep deficiency prob-lem and has not yet acknowledgedthat potential problem.”

The report said that aviation main-tenance personnel probably are un-aware of how little they sleep incomparison with the amount of sleeprecommended by specialists.

The report recommended the follow-ing actions to help maintenance per-sonnel improve their sleeping habits:

• Airlines could provide monitoringequipment to maintenance person-nel to help them understand theirsleeping habits and to improvethem, if necessary. “The produc-tivity return on investment wouldquickly justify the cost of theequipment, administration person-nel and training,” the report said;

• An educational campaign couldbe organized to show that ade-quate sleep — along with avoid-ing abuse of alcohol or drugs —is an essential element of a main-tenance employee’s fitness forduty; and,


• Information could be providedto inform maintenance personnelof the symptoms of fatigue andto provide recommendations toeliminate or lessen the problem.“If personnel can recognize fa-tigue, they can help one anotherto avoid the inevitable perfor-mance degradation and potentialerror,” the report said. The reportsaid that the Air Transport Asso-ciation of America includedsuch recommendations in itsAlertness Management Guide,published in 2000. The recom-mendations called for minimiz-ing sleep loss; altering habits toacquire the necessary amount ofsleep; creating an acceptable en-vironment for sleep; and under-standing the effects on sleep ofage, alcohol, diet and exercise.7

The report also recommended thefollowing actions involving work-place temperatures, light levels andsound levels:

• The effects of working in condi-tions that combine high ambienttemperatures, a hot ramp, hotaircraft and hot ground equip-ment can be lessened with“adequate staffing, reasonablescheduling of activity, properpacing in high-temperatureconditions, plenty of water andadequate rest throughout thework shift,” the report said.

The average 86-degree F tem-perature experienced by themaintenance personnel whowore monitoring equipmentexceeded the maximum temper-atures recommended by FAA’sThe Human Factors Guide forAviation Maintenance and In-spection. The recommendedtemperatures vary from about 66degrees F (19 degrees C) to 79degrees F (26 degrees C), de-pending on a variety of factors,including temperature, humidity,air velocity, the type of work be-ing performed and the type ofclothing worn by the worker.8

Nevertheless, the report said thatthe companies participating inthe study complied with mostrecommended practices for hot-weather work: Drinking waterwas readily available, and fansand portable air-conditioningsystems were in place;

• High sound levels are “an un-avoidable byproduct of turbineengines and industrial repairequipment,” the report said. Thereport recommended hearingprotection (earplugs and/or head-phones) for workers exposed tosound levels that exceed standardsset by the U.S. OccupationalSafety and Health Administration(OSHA). The sound levels record-ed by the monitoring equipmentworn by maintenance personnel


were within OSHA limits. Be-cause maintenance personnelwore the monitoring equipmentwithout supervision, there was noindication of when they worehearing protection. Nevertheless,researchers observed maintenancepersonnel — especially ramp per-sonnel — wearing hearing protec-tion when required; and,

• The report recommended ade-quate lighting in the workplace.The average light level of 692lumens per square meter recordedby the monitoring equipment wornby maintenance personnel was lessthan the range of 750 lumens persquare meter to 1,000 lumens persquare meter recommended byThe Human Factors Guide for Avi-ation Maintenance and Inspection.

The evaluation described in the reportwas one element of an ongoing studyof the effects of the workplace envi-ronment and fatigue on work per-formance. Additional research wasplanned to gather data to be used indeveloping models to predict when acombination of fatigue and envi-ronmental factors in the workplacewould be likely to result in humanerror. The report said that the data alsowill be used to develop guidelines tohelp maintenance personnel preventor reduce their fatigue and correctproblems in the workplace environ-ment that are within their control.♦

Notes1. FSF Editorial Staff. “Heredity,

Disease, Aging Present Crew-members With Increased Risk ofHearing Loss.” Human Factors& Aviation Medicine Volume 47(July–August 2000): 3.

2. U.S. National Institute ofOccupational Safety andHealth. NIOSH Sound Meter.www.cdc.gov/niosh/hp140.html.

3. The report said that the light mea-surement might be misleading insome situations, including situa-tions involving reduced light, situ-ations in which a flashlight is usedand situations involving mainte-nance procedures that require per-sonnel to look inside a cowling.The report also said that the sen-sor measured the amount of lighton the person wearing the moni-toring equipment rather than theamount of light on the work be-ing performed by that person;nevertheless, the report said thatin most situations, those measure-ments would be similar.

4. Brautigam, Jack. CompactFluorescent Lamps. WashingtonState University CooperativeExtension. cru.cahe.wsu.edu/CEPub l i ca t i ons / eb1845e /eb1845e.html. Nov. 12, 2001.

5. Sian, B.; Watson, J. Study of Fa-tigue Factors Affecting Human


Performance in Aviation Main-tenance. Washington, D.C., U.S.:U.S. Federal Aviation Adminis-tration (FAA) Office of AviationMedicine, 1999.

6. Battelle Memorial Institute;JIL Information Systems. AnOverview of the ScientificLiterature Concerning Fatigue,Sleep, and the Circadian Cycle.Washington, D.C. U.S.: FAAOffice of the Chief Scientific andTechnical Advisor for HumanFactors, 1998.

7. Air Transport Association ofAmerica (ATA); Alertness Solu-tions. Alertness ManagementGuide. Washington, D.C., U.S.:ATA, 2000.

8. FAA. The Human Factors Guidefor Aviation Mainte-nance and In-spection. Edited by Maddox, M.Washington, D.C., U.S., 1998.

[FSF editorial note: This article,except where specifically noted, isbased on Evaluation of AviationMaintenance Working Environ-ments, Fatigue and Human Per-formance, a product of the U.S.Federal Aviation Administration(FAA) Human Factors Issues inAircraft Maintenance and Inspec-tion Research Program. The report

was written by William B. Johnsonand Felisha Mason of Galaxy Sci-entific, Steven Hall of Embry-Riddle Aeronautical University andJean Watson of FAA. The 44-pagereport contains figures, tables andappendixes.]

Further Reading FromFSF Publications

Hobbs, Alan; Williamson, Ann.“Survey Assesses Safety Attitudesof Aviation Maintenance Personnelin Australia.” Aviation MechanicsBulletin Volume 48 (November–December 2000).

Caldwell, J. Lynn. “Managing Sleepfor Night Shifts Requires PersonalStrategies.” Human Factors & Avia-tion Medicine Volume 46 (March–April 1999).

FSF Editorial Staff. “OvercomingEffects of Stress Offers GreatestOpportunity to Sleep Well.” HumanFactors & Aviation MaintenanceVolume 45 (July–August 1998).

Flight Safety Foundation FatigueCountermeasures Task Force. “Prin-ciples and Guidelines for Duty andRest Scheduling in Corporate andBusiness Aviation. Flight Safety Di-gest Volume 16 (February 1997).


MAINTENANCE ALERTS

NTSB RecommendsChanges in Lubricationof Horizontal StabilizerTrim System on DC-9,MD-80/90, Boeing 717

The U.S. National TransportationSafety Board (NTSB), citing a Jan.31, 2000, accident in which anAlaska Airlines McDonnell DouglasMD-83 struck the Pacific Ocean, hasrecommended changes in the lubri-cation procedure and the end-playcheck procedure for the horizontalstabilizer trim system of DouglasDC-9, MD-80/90 and Boeing 717series airplanes.

The MD-83, which was beingflown from Puerto Vallarta, Mexico,to Seattle, Washington, U.S., was de-stroyed in the accident, and all 88people in the airplane were killed.The investigation of the accident wascontinuing when NTSB issued therecommendations.

The horizontal stabilizer onMD-80/90, DC-9 and B-717 seriesairplanes is at the top of the verticalstabilizer and is hinged near thetrailing edge to allow the leadingedge to move up and down to providepitch trim. The horizontal stabilizer’sactuating mechanism is an “acme

screw” — a threaded shaft that is at-tached to the horizontal stabilizer andthat rotates through a stationary acmenut attached to the vertical stabilizer.The acme screw is rotated by an elec-tric motor activated by the autopilotor by a control-wheel trim switch.

NTSB said, “Performance data basedon the accident airplane’s flight datarecorder indicate that the leadingedge of the horizontal stabilizer ro-tated upward well beyond its designlimit. Examination of the acme screwand [acme] nut … revealed that ap-proximately 90 percent of the acmenut threads had worn away before theremainder of the acme nut threadsstripped out. Those remnants werefound wrapped around the acmescrew. The stripping of these threadswould have allowed the acme screwto slip upward through the acme nutuntil the lower stop impacted thebottom of the acme nut.”

NTSB said that its review of design-and-certification data revealed that“no contingency for stripped acmenut threads was incorporated into thedesign for the horizontal stabilizertrim system on these airplanes.Thus, the possibility of the acmescrew disengaging from the acme nutwas not formally considered duringthe certification process.”


Maintenance manuals for DC-9,MD-80/90 and B-717 series airplanessay that grease should be applied pe-riodically to acme nut fittings, that alight coat of grease should be brushedonto the acme screw thread and thatthe grease should be distributed overthe length of the acme screw by op-erating the system through its fullrange of travel. Improper lubricationof acme screw and acme nut assem-blies can result in excessive acme nutthread wear rates, NTSB said.

NTSB said that its investigators ob-served differences in the methodsused by maintenance personnel tolubricate acme screw and acme nutassemblies and that some methodsdid not apply grease to the entirelength of the acme screw.

“As a result, [NTSB] is concernedthat the current lubrication proceduremay not be adequate to ensure con-sistent and thorough lubrications ofthe acme screw and [acme] nut as-sembly by all operators,” NTSB said.

Seven months after the accident, onAug. 23, 2000, NTSB issued airwor-thiness directive (AD) 2000 15-15outlining the required procedure to beused in monitoring wear of the acmenut thread. NTSB said that, sincethen, its investigators have observedmaintenance personnel performing theprocedure, called an end-play check,and have reviewed data indicating that

the end-play check may not be “ade-quate to ensure consistent, accurateand reliable measurements of acmescrew and [acme] nut wear.”

NTSB said that during the accident in-vestigation, some inspectors andmanagers from the U.S. Federal Avia-tion Administration (FAA) said thatthe monitoring of airline lubricationpractices might not be adequate to en-sure that only compatible mixtures ofgrease are used on the acme screw andacme nut assemblies. (When incom-patible mixtures of grease are used,their physical properties or their per-formance may be affected adversely.)

In a letter to FAA, NTSB said thatFAA should:

• Require Boeing Commercial Air-planes to revise the lubricationprocedure for the horizontal sta-bilizer trim system on DC-9,MD-80/90 and B-717 series air-planes “to minimize the probabil-ity of inadequate lubrication”;

• Require Boeing to revise theend-play check procedure “tominimize the probability of mea-surement error” and to conducta study to “validate the revisedprocedure against an appropriatephysical standard of actual acmescrew and acme nut wear”;

• Require specialized training formaintenance personnel who


lubricate the horizontal stabilizertrim system on DC-9, MD-80/90and B-717 series airplanes;

• Require specialized training formaintenance personnel who in-spect the horizontal stabilizertrim systems on DC-9, MD-80/90and B-717 series airplanes. Thetraining should include familiar-ization with the end-play check;

• Require operators that proposechanges in lubrication appli-cations to first provide FAAwith technical data to show thatthe proposed changes “will notpresent any potential hazards”and to obtain FAA approval ofthe proposed changes;

• Provide guidance to principalmaintenance inspectors “to noti-fy all operators about the poten-tial hazards of using inappropriategrease types and mixing incom-patible grease types”;

• Survey operators to determinewhether lubrication processesare being used that deviate frommanufacturer specifications. Ifany of the deviations involve useof inappropriate grease types orincompatible grease mixtures,eliminate those processes; and,

• Convene an industrywide forumto discuss lubrication of aircraft

components, “including the qual-ification, selection, applicationmethods, performance, inspec-tion, testing, and incompatibili-ty of grease types used on aircraftcomponents.”

ATSB RecommendsReview of

Lubrication inLanding-gearComponents

The Australian Transport Safety Bu-reau (ATSB), citing landing gearfailures on two Boeing 737s, has rec-ommended that the lubrication ofpin/lug joints in main-landing-gearstructures be reviewed “to ensure thatmovement between pins and lugs iseffectively lubricated.”

ATSB said that components of themain landing gear on two B-737sfailed when the landing gear werebeing extended. Both incidents oc-curred during landings in Melbourne,Australia; the first incident occurredMarch 12, 1999, and the second inci-dent occurred April 4, 1999.

“On both occasions, the landinggear extended and locked normally,”ATSB said in a technical analysisreport on the incidents. “However,while landing was completedwithout incident, the uncontrolledmovement of fractured landing-gear


components has the potential to dam-age other components and interferewith flight controls.”

In one incident, an aileron bus cablewas damaged during the landing-gearextension.

In a similar incident in 1987, anactuator-beam arm-lug fitting on aB-737 broke and the released com-ponents interfered with the move-ment of aileron cables, resulting inan uncommanded maneuver, thereport said. [The report did not saywhere the incident occurred.] Afterthat incident, modifications wereimposed in lug bushes and the meth-ods used to install them.

“The [Australian] occurrences … in-dicate a continuing deficiency in thesafety system that addresses the struc-tural integrity of landing gear,” thereport said.

The report said that the fractures of thelanding-gear-component lugs were aresult of stress corrosion cracking,which occurred because “componentsmanufactured from specific alloys[were] exposed to a particular environ-ment while being subjected to a sus-tained tensile stress state.

“The high-strength steel alloysrequired for the manufacture oflanding-gear components are knownto be susceptible to stress corrosion

cracking when exposed to the normaloperating environment of landinggear (moisture, [especially] salt-laden moisture),” the report said.“Landing-gear components are alwayssubjected to sustained tensile stressesthrough the residual stresses that arecreated by the manufacturing process-es (e.g., forging, heat treatment).”

Cadmium plating and paint filmstypically are used to avoid stresscorrosion cracking by providing aphysical barrier between the steel al-loy and the environment. Neverthe-less, the contact stresses and relativemovements of contacting surfaces inthe pin-lug joints preclude the use ofcadmium plating and paint films. In-stead, replaceable bushings are fittedto the lugs to isolate the lug surfacefrom the operating environment.

“The failure of lugs in landing-gearpin/lug joints by stress corrosioncracking indicates that the designeddefense against stress corrosioncracking has been defeated,” the re-port said. “The failure of the lugsshould be attributed to the failure ofthe environmental isolation system.”

Inspection of the pin/lug joints in theincident airplanes revealed that a gaphad been created between the bushingand the lug and that stress corrosioncracking initiated at the surface of thelugs. The inspection showed thatgalling (which ATSB described as


“adhesive wear [that] occurs whenwelding and subsequent fracture occursbetween the surface asperities of twosurfaces subjected to high contact pres-sure and limited sliding movement”)had occurred between the wearing sur-faces of the pins and bushings whenthe landing gear was being operated.

Lubrication of the area to ensure sep-aration of sliding surfaces is essen-tial in preventing galling.

ATSB said that “consideration shouldbe given to verifying the adequacy ofgrease paths to allow grease to lubri-cate all contact surfaces within a joint.In particular, the conditions underwhich grease can flow to all surfacesshould be established. Greasing whilecomponents are under load may ex-clude grease from regions of contact.Localized grease exclusions may besignificant in joints that experience alimited range of movement.”

Engine Failure PromptsEmergency Landing ofTwin-engine Islander

The pilot of a Pilatus Britten-NormanBN-2B-26 Islander said that he hadleveled the airplane at 3,000 feet af-ter a night departure from Glasgow,Scotland, when he heard a noise thatsounded like “hailstones striking thewindscreen.” The right engine (a Ly-coming O-540-E4C5 piston engine)

lost power, and the pilot declared anemergency, flew the airplane back tothe departure airport and conducteda single-engine landing.

Inspection of the right engine revealedthat although the engine was not turn-ing, the propeller could be rotated, thatthere was a hole in the lower forwardface of the crankcase and that thecrankshaft had failed in the area of theno. 1 journal bearing. Inspection alsoshowed that the no. 4 inlet valve push-rod tube was bent, that there was a holein the no. 4 cylinder rocker cover andthat the no. 1 piston connecting-rodend cap and debris from the crankcasewere in the lower cowling.

The U.K. Air Accidents InvestigationBranch (AAIB) said that after the rock-er covers were removed, a fracture wasobserved across the diameter of the no.4 inlet valve spring upper seat. Thefracture caused the valve to enter thecylinder. A similar fracture occurred inthe valve spring upper seat of the no. 6cylinder, but half of the seat remainedin position, as did the valve stem.

The engine had accumulated 8,564hours since new and 1,453 hourssince the last overhaul, about 2 1/2years before the accident.

A metallurgical examination revealedthat the crankshaft had failed “as aresult of long-term high-cycle tensionfatigue” at the no. 1 connecting-rod


crank pin and that a fatigue crack hadprogressed through about 75 percentof the crank-pin cross section. Thereport said that the fracture pro-gressed through the lubrication sup-ply hole and that, as the fracturewidened, oil pressure decreased.

The report said, “Measurement of allthe crankshaft journals (i.e., mainsand crank pins) showed that they hadbeen ground 0.006 inch [0.152 milli-meter] undersize. Microhardnesstests were conducted on a sample ofmaterial that included the bearingradius in which the crankshaft frac-ture had initiated. The hardness wasfound to be low for a nitrided surface,indicating that it had not been reni-trided after being ground undersize.”

(The renitriding requirements werespecified in Textron LycomingService Bulletin [SB] 222D, datedNov. 8, 1999. The SB said that allreground crankshafts should berenitrided but that polishing to0.006 inch undersize was permitted.The report said that the companyconsiders SB 222D mandatory butthat neither the U.S. FederalAviation Administration (FAA) northe U.K. Civil Aviation Authority(CAA) requires compliance. Never-theless, the report said that the reni-triding requirements in the SB werethe same as those included in theengine overhaul manual, which waslast amended in 1971.)

“Although the reason for the fatigueinitiation was not fully established, thereduced surface hardness in the fail-ure region of the crank pin radius, cou-pled with the engine manufacturer’sview on the importance of maintain-ing the hardened nitrided layer, impliedthat the apparent failure to renitridethe crankshaft after grinding couldhave been a factor,” the report said.

Maintenance records showed that theengine was overhauled in 1988 by themanufacturer and that Lycoming hadsaid that the engine had a “reworkedcrankshaft, serial number B2379,part number LW-17622.” Subsequentoverhauls were performed in 1992and 1997; in both instances, there wasno record of the crankshaft serialnumber or part number. (Joint Avia-tion Requirements [JARs] do not re-quire that the numbers be recorded.)

AAIB was unable to obtain recordscontaining details of the work per-formed during the 1988 overhaulbecause FAA requires such recordsto be kept for only two years and, asa result, the records had been de-stroyed. JARs Part 145.55 includes asimilar two-year requirement.

As a result of the investigation, AAIBrecommended that CAA “promoteamendment of JARs 145.55 to in-crease the minimum period for theretention of maintenance recordsfrom two [years] to five years.”♦


NEWS & TIPS

Conference onQuality in CommercialAviation To Be Held in

September 2002

The U.S. Federal Aviation Adminis-tration and the Aviation/Space andDefense Division of the AmericanSociety for Quality have scheduledtheir 13th Conference on Qualityin Commercial Aviation (CQCA)for Sept. 22–25, 2002, in Dallas,Texas, U.S.

The conference, which is held every18 months, will include internationalrepresentatives from airlines, suppli-ers to the aviation industry, manu-facturers of aircraft and aircraftengines, FAA and other civil avia-tion authorities. Presentations willdiscuss safety, quality and mainte-nance issues.

The International Aerospace QualityGroup (IAQG), which supports theCQCA, will hold its Supplier Gener-al Assembly meeting in Dallas be-ginning Sept. 25, immediately afterthe CQCA.

For more information: Lester G.Lemay, CQCA, 5400 Bosque Blvd.,Suite 680, Waco TX 76710 U.S. Tele-phone: +1 (254) 776-3550.

BrushlessTorque-controlled

Screwdriver EliminatesCarbon Dust

A torque-controlled screwdriverwith a brushless motor has beendesigned to eliminate carbon dustand to last longer, said the manu-facturer, ASG.

The screwdriver is rated for continu-ous use with minimal heat buildup,the manufacturer said. The screw-driver is designed for medium-torqueassembly applications to light-torqueassembly applications and stops

Torque-controlled Screwdriver


automatically when a preset torqueis achieved. The 7.95-inch (20-centimeter), 12.7-ounce (360-gram)screwdriver can be converted from alever-start screwdriver to a push-to-start screwdriver.

For more information: ASG, 15700 S.Waterloo Road, Cleveland, OH 44110U.S. Telephone: +1 (216) 486-6163.

Lightweight Solid-wallSwaged Inserts

Designed for Use inAircraft Engines

A variety of lightweight solid-wallswaged inserts have been designedfor use in aircraft engines and otheraerospace applications, said the man-ufacturer, SPS Technologies.

The inserts are available in variousalloy-steel materials with various

finishes, are intended to improvethread life and thread performance,and include a locking knurl design toaid in installation.

For more information: SPS Tech-nologies, 301 Highland Ave.,Jenkintown, PA 19046-2692 U.S.Telephone: +1 (215) 572-3718.

Stripping AgentsRemove Silicon,Polysulfide From

Aircraft

Two aircraft grades of GenSolvehigh-performance stripping agentallow removal of silicone andpolysulfide sealants and coatingsfrom aircraft metal, glass, ceramicand plastic components, said the man-ufacturer, General Chemical Corp.

The GenSolve stripping agentsbreak down sealants so that they canbe rinsed away without damage toaircraft components. The strippingagents can be sprayed on, wiped onor used in immersion cleaning sys-tems. They do not react with copper,iron, aluminum, zinc or titanium.

For more information: Fine Chemi-cals Group, General Chemical Corp.,90 East Halsey Road, Parsippany, NJ07054 U.S. Telephone: (800) 631-8050 (U.S.) or +1 (973) 515-0900.Solid-wall Swaged Inserts


Leak-detectionTechnology Tests

Deicing Fluid, Fuels

Vista Research’s non-invasive leak-detection technology is being usedto test aircraft deicing fluid andaircraft fueling systems, said themanufacturer.

The Vista system calculates the ex-pected change in fluid volume as airconditions and ground conditionscause the temperature of pipeline con-tents to change. If changes in fluidvolume do not conform to the expect-ed changes, the discrepancy indicatesthat a leak exists. The leak can be lo-cated by sensors attached to the pipe.

For more information: Vista Research,755 North Mary Ave., Sunnyvale,CA 94085 U.S. Telephone: +1 (408)830-3300.

Inspection CameraFits Through

Narrow Openings

The PTZ-Cam 2.75 robotic inspec-tion video camera fits throughnarrow openings to evaluate thestructural condition of a vessel, saidthe manufacturer, iShot Imaging.

The camera has a total zoom capa-bility of 40-to-1, and the camera’shead assembly pans 360 degrees and

tilts plus or minus 110 degrees. Thecamera is equipped with twin spotlamps and twin flood lamps for evenillumination without shadows, and aremote control console for manycamera functions.

For more information: iShot Imaging,27 Ironia Road, Flanders, NJ 07836U.S. Telephone: +1 (973) 927-2900.

Instrument MeasuresTension Ultrasonically

The StressTel BoltMike III ultra-sonically measures the tension andclamp load of threaded fasteners in thetightening of critical bolted joints inaircraft engines and the verification oftension on bolts on clamping wheelassemblies, said the manufacturer.

The instrument weighs 2.5 pounds(1.14 kilograms), operates for as longas 40 hours on standard double-A

Ultrasonic Tension Meter


batteries and has rapid calibrationand setup, the manufacturer said.

For more information: StressTel,2790 West College Ave., StateCollege, PA 16801-2605, U.S. Tele-phone: +1 (814) 861-6300.

ElectrostaticOil-cleaning Systems

Remove Contaminants

KLEENTEK electrostatic oil-cleaning systems remove insolublecontaminants, including tars andvarnishes, from hydraulic oil systems,said the manufacturer.

Tar, varnish and sludge on componentsurfaces can cause a loss of controlstability, requiring repeated valveadjustments, increased downtime andreduced machine performance. Theoil-cleaning systems draw contami-nants out of the oil and trap them onthe surface of the collector, the man-ufacturer said.

For more information: Kleentek,4440 Creek Road, Cincinnati, Ohio45242 U.S. Telephone: (888) 281-4888 (U.S.) or +1 (513) 891-0400.

Tapes ProtectAircraft Surfaces

Colored self-adhering tapes havebeen introduced to replace top-coat

paints on aircraft surfaces, saidthe manufacturer, 3M EngineeredAdhesives Division.

The tapes are easy to apply, provideprotection for interior surfaces andexterior surfaces, and resist accumu-lation of surface contaminants. Thetapes require little maintenance andresist degradation or discolorationcaused by exposure to ultravioletlight.

Paint Replacement Tape

For more information: 3M Engi-neered Adhesives Division, 3MCenter, Building 220-8E-05, St. Paul,MN 55144-1000 U.S. Telephone:(800) 364-3577 (U.S.) or +1 (651)733-1110.♦

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Documents

Fatigue Evaluation Indicates Most Aviation Maintenance ... · Fatigue Evaluation Indicates Most Aviation Maintenance Personnel Obtain Insufficient Sleep An FAA evaluation of the effects