Aircraft Icing Jim Vasilj, Meteorologist Center Weather Service Unit Auburn, Washington NOAA/NWS Seattle Center Weather Service Unit (ZSE)

Aircraft IcingAircraft Icing

Jim Vasilj, MeteorologistJim Vasilj, Meteorologist

Center Weather Service UnitCenter Weather Service Unit

Auburn, WashingtonAuburn, Washington

NOAA/NWS Seattle Center Weather Service Unit (ZSE)NOAA/NWS Seattle Center Weather Service Unit (ZSE)

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• NOTNOT caused by caused by iceice in clouds. in clouds.

• IsIs caused by “ caused by “super-cooledsuper-cooled” ” liquidliquid water droplets in clouds…water droplets in clouds…– That strike the leading edge of an airfoil andThat strike the leading edge of an airfoil and– Freeze on impactFreeze on impact

• Aircraft must be in clouds or Aircraft must be in clouds or precipitation (visible water droplets) for precipitation (visible water droplets) for icing to occuricing to occur

Review of Causes of IcingReview of Causes of Icing


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Combined EffectsCombined Effects


Pilot Action RecommendationPilot Action Recommendation: Watch your outside air temperature and try : Watch your outside air temperature and try to stay out of visible moisture (precipitation or clouds) anytime the to stay out of visible moisture (precipitation or clouds) anytime the temperature is below 0°C. In some instances the moisture can almost be temperature is below 0°C. In some instances the moisture can almost be invisible. invisible. Remember…on a standard day you lose about 2°C per thousand Remember…on a standard day you lose about 2°C per thousand feet.feet.

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• Liquid water content (LWC)Liquid water content (LWC)

• TemperatureTemperature

• Droplet sizeDroplet size

• Cloud typeCloud type

• Airfoil geometryAirfoil geometry

• AirspeedAirspeed

• Duration of exposureDuration of exposure

Icing Severity FactorsIcing Severity Factors


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Ice formation requires Ice formation requires

both water drops below both water drops below

freezing (0°C to -40°C) freezing (0°C to -40°C)

and a and a nucleation pointnucleation point..

•This can be an impurity This can be an impurity

in the water (eg, dust or in the water (eg, dust or

minerals) or ice crystals.minerals) or ice crystals.

•When the molecules When the molecules

align properly (this align properly (this

could be due to a jolt), could be due to a jolt),

ice will begin to form.ice will begin to form.

““Super-Cooled” Water Super-Cooled” Water FormationFormation


Source: www.gifbay.com via giphy.comSource: www.gifbay.com via giphy.com

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TemperatureTemperature

http://www.casa.gov.au/fsa/2006/apr/26-33.pdf

Most icing Most icing occurs occurs betweenbetween00°° and -20 and -20°°CC


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Types of IcingTypes of Icing

• ClearClear

• MixedMixed

• RimeRime

ClearClear 0° to -10°C0° to -10°C(32° to 14°F)(32° to 14°F)

MixeMixedd

-10° to -15°C-10° to -15°C(14° to 5°F)(14° to 5°F)

RimeRime -15° to -40°C-15° to -40°C(5° to -40°F)(5° to -40°F)

TemperatureTemperature Range Range

Frequency of OccurrenceFrequency of Occurrence


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Clear IcingClear Icing

• Transparent, “Glossy”Transparent, “Glossy”

• Not easily seen at firstNot easily seen at first

• Can spread out on Can spread out on

airfoil beyond “reach” airfoil beyond “reach”

of de-icing equipmentof de-icing equipment

• Hard, heavy, and Hard, heavy, and

tenacioustenacious


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Clear IcingClear Icing

• Tends to form Tends to form ‘Horns’ at leading ‘Horns’ at leading edge of airfoil.edge of airfoil.

Gray is region Gray is region where air iswhere air isstagnant.stagnant.

• More difficult to More difficult to remove with de-icing remove with de-icing equipment.equipment.

• Disrupts and makes Disrupts and makes airflow more turbulentairflow more turbulent

No IcingNo Icing


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The super-cooled water is forming ice as it hits the The super-cooled water is forming ice as it hits the

already frozen ice cube, similar to Clear Icing.already frozen ice cube, similar to Clear Icing.

Icing Accretion ExampleIcing Accretion Example


Source: www.gifbay.com via giphy.comSource: www.gifbay.com via giphy.com

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Rime IcingRime Icing

• Is opaque Is opaque • Easily seenEasily seen• Lighter than clear iceLighter than clear ice• However…shape and However…shape and

rough surface rough surface decrease aircraft decrease aircraft aerodynamicsaerodynamics

• Easier to remove Easier to remove than clear icethan clear ice


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Rime IcingRime Icing

• Tends to form at Tends to form at leading edge of airfoilleading edge of airfoil

• Easier for deicing Easier for deicing equipment to removeequipment to remove

Gray is region Gray is region where air iswhere air isstagnant.stagnant.

RimeRime

• Compare with Compare with ‘horns’‘horns’ of clear icing.of clear icing.

ClearClear


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Mixed IcingMixed Icing

• Mixture of Clear and Rime iceMixture of Clear and Rime ice

• Easily seen at firstEasily seen at first

• Forms when water drops vary Forms when water drops vary

in size or when liquid drops in size or when liquid drops

are intermingled with snow are intermingled with snow

and iceand ice

• Same hazards as Clear icing…Same hazards as Clear icing…

– Can spread out on airfoil beyond Can spread out on airfoil beyond

“reach” of de-icing equipment“reach” of de-icing equipment


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Mixed Mixed IcingIcing

• Also tends to form Also tends to form ‘Horns’ at leading ‘Horns’ at leading edge of airfoil.edge of airfoil.

• More difficult to More difficult to remove with de-remove with de-icing equipment.icing equipment.



• Warm, moist air over-running cold Warm, moist air over-running cold airair

• Precipitation begins as snow, Precipitation begins as snow, changes to rainchanges to rain– Then falls through Cold airThen falls through Cold air– Becomes “Super-Cooled Water”Becomes “Super-Cooled Water”– Freezes on impactFreezes on impact

• Heavy icing in a short period of Heavy icing in a short period of timetime

• Best maneuver Best maneuver maymay be to gain be to gain altitudealtitude– Check with a weather briefer first!Check with a weather briefer first!

Freezing RainFreezing Rain

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Typical Freezing Typical Freezing Rain/Sleet SoundingsRain/Sleet Soundings


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American Eagle #4184American Eagle #4184


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• 31 October 199431 October 1994

• An ATR-72 was scheduled to 4:10pm An ATR-72 was scheduled to 4:10pm departure from IND to ORDdeparture from IND to ORD

• Entered holding pattern at 10,000ftEntered holding pattern at 10,000ft

• Flight Data Recorder recorded Flight Data Recorder recorded activation of Level III de-icing during activation of Level III de-icing during decent to 10,000ftdecent to 10,000ft



• Ridge of ice accreted beyond the Ridge of ice accreted beyond the deicing boots during freezing deicing boots during freezing rain/drizzle in holding patternrain/drizzle in holding pattern

• The airplane went into a roll, The airplane went into a roll, followed by a rapid decent due to followed by a rapid decent due to the cumulative effects of clear ice.the cumulative effects of clear ice.

• 68 people died near Roselawn IN.68 people died near Roselawn IN.

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A field near Roselawn, Ind., was strewn with debris A field near Roselawn, Ind., was strewn with debris including a portion of the red, white and blue tail including a portion of the red, white and blue tail section of American Eagle Flight 4184, after it crashed section of American Eagle Flight 4184, after it crashed on Oct. 31, 1994, killing all 68 people aboard. on Oct. 31, 1994, killing all 68 people aboard. Wreckage of the 7-month-old twin-engine propjet was Wreckage of the 7-month-old twin-engine propjet was scattered across a muddy 40-acre soybean field in scattered across a muddy 40-acre soybean field in Northwest Indiana 30 miles south of Gary. (Photo: Northwest Indiana 30 miles south of Gary. (Photo: Charles Bennett / Associated Press) Charles Bennett / Associated Press) via Indianapolis via Indianapolis StarStar

Crash investigators search the site Crash investigators search the site of the crash of American Eagle flight of the crash of American Eagle flight 4184 in a field near Roselawn, Ind. 4184 in a field near Roselawn, Ind. in the days after the Oct. 31, 1994 in the days after the Oct. 31, 1994 crash.crash.

Associated Press file Associated Press file via Daily via Daily HeraldHerald

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Situational AwarenessSituational Awareness

• Keep current with the Keep current with the weather in your areaweather in your area

• Know where the fronts Know where the fronts are locatedare located

• Keep current with Keep current with freezing levels in your freezing levels in your areaarea

http://adds.aviationweather.gov/airmets/http://adds.aviationweather.gov/airmets/

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• Know the cloud bases.Know the cloud bases.

• Know the cloud tops…light, non-turbo aircraft Know the cloud tops…light, non-turbo aircraft may not be able to climb above 8,000 ft. Once may not be able to climb above 8,000 ft. Once on top…can they stay there?on top…can they stay there?

• Are clouds air mass or frontal? Frontal clouds Are clouds air mass or frontal? Frontal clouds cover larger areas…aircraft flying through cover larger areas…aircraft flying through frontal clouds may experience icing conditions frontal clouds may experience icing conditions for a longer period of time.for a longer period of time.

• Are alternate routes available, ie, around fronts Are alternate routes available, ie, around fronts or around mountains?or around mountains?

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CurrentCurrent ...FL030 to FL300 including ...FL030 to FL300 including SLD.SLD.

ForecastForecast … 0 to 18 hours 010 to … 0 to 18 hours 010 to FL290FL290(SLD…Super-cooled Large Drops)(SLD…Super-cooled Large Drops)

• Know current and forecast icing Know current and forecast icing potentialpotential

http://www.aviationweather.gov/http://www.aviationweather.gov/icing/fip icing/fip

Delineates general areas of icing potentialDelineates general areas of icing potential

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You Should KnowYou Should Know

• In In mostmost freezing rain episodes, a climb to freezing rain episodes, a climb to warmer air aloft is in order.warmer air aloft is in order.

• Heavy accumulation of ice can occur in Heavy accumulation of ice can occur in cumulus clouds. Get out of these clouds and cumulus clouds. Get out of these clouds and into VFR conditions immediately.into VFR conditions immediately.

• In stratiform clouds, a change in altitude is in In stratiform clouds, a change in altitude is in order to a flight level with above freezing order to a flight level with above freezing temperatures, one where the temperature is temperatures, one where the temperature is colder than -10°C, or a level above and out of colder than -10°C, or a level above and out of the clouds.the clouds.

• It is considered best to begin avoidance when It is considered best to begin avoidance when icing is first detected.icing is first detected.

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Seattle CWSUSeattle CWSUhttp://www.wrh.noaa.gov/zse/http://www.wrh.noaa.gov/zse/

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Seattle CWSUSeattle CWSUhttp://www.wrh.noaa.gov/zse/http://www.wrh.noaa.gov/zse/

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Seattle CWSUSeattle CWSUhttp://www.wrh.noaa.gov/zse/icing_fcst.phphttp://www.wrh.noaa.gov/zse/icing_fcst.php

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NOAA/NWS Seattle Center Weather Service Unit (ZSE)NOAA/NWS Seattle Center Weather Service Unit (ZSE)*

Seattle CWSUSeattle CWSUhttp://www.wrh.noaa.gov/zse/http://www.wrh.noaa.gov/zse/mobile.phpmobile.php

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http://www.wrh.noaa.gov/zse/swipe.phphttp://www.wrh.noaa.gov/zse/swipe.php


Oakland CWSUOakland CWSUhttp://www.wrh.noaa.gov/zoa/MOBILE/ZOA2.htmhttp://www.wrh.noaa.gov/zoa/MOBILE/ZOA2.htm

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NWS Mobile WeatherNWS Mobile Weatherhttp://mobile.weather.gov/http://mobile.weather.gov/

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NWS RAP/RUC NWS RAP/RUC Analyses/ForecastsAnalyses/Forecasts

http://ruc.noaa.gov/soundings/http://ruc.noaa.gov/soundings/

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Fog/Clouds LikelyFog/Clouds LikelyHQM had 2-3sm HQM had 2-3sm Visibility andVisibility and014-016 Ceiling 014-016 Ceiling DevelopingDeveloping

Red: Temperature Red: Temperature (°C)(°C)Blue: Dew Point Temp Blue: Dew Point Temp

(°C)(°C)

Altitude (ft)Altitude (ft)Wind Speed Wind Speed (kt)(kt)

Change Change forecast forecast timetime

In general, look for Temperature-Dew Point to be less than 6°C for clouds.In general, look for Temperature-Dew Point to be less than 6°C for clouds.

NWS RAP/RUC NWS RAP/RUC Analyses/ForecastsAnalyses/Forecasts

http://ruc.noaa.gov/soundings/http://ruc.noaa.gov/soundings/

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Saturated below 15,000ftSaturated below 15,000ftKILM 241653Z 01008KT 5SM -KILM 241653Z 01008KT 5SM -FZRA BR OVC009 M02/M04 FZRA BR OVC009 M02/M04 A3014 AO2 A3014 AO2 UPB46E49FZRAE46B49 SLP204 UPB46E49FZRAE46B49 SLP204 P0005 I1006 T10221039P0005 I1006 T10221039

Red: Temperature Red: Temperature (°C)(°C)Blue: Dew Point Temp Blue: Dew Point Temp

(°C)(°C)

Altitude (ft)Altitude (ft)Wind Speed Wind Speed (kt)(kt)

Icing Icing SIGMET SIGMET 120-FL180120-FL180

0°C0°C

WSUS02 KKCI 241629 WS2Y MIAY WS 241629 SIGMET WSUS02 KKCI 241629 WS2Y MIAY WS 241629 SIGMET YANKEE 1 VALID UNTIL 242029 NC SC AND CSTL WTRS YANKEE 1 VALID UNTIL 242029 NC SC AND CSTL WTRS FROM 20WNW ECG TO 70SE ECG TO 90ESE CHS TO FROM 20WNW ECG TO 70SE ECG TO 90ESE CHS TO 30SSW FLO TO 20WNW ECG OCNL SEV RIME/MXD ICGICIP 30SSW FLO TO 20WNW ECG OCNL SEV RIME/MXD ICGICIP BTN 120 AND FL180. CONDS CONTG BYD 2029Z.BTN 120 AND FL180. CONDS CONTG BYD 2029Z.*

Aviation Weather CenterAviation Weather Centerhttp://www.aviationweather.gov/icinghttp://www.aviationweather.gov/icing

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Aviation Weather CenterAviation Weather Centerhttp://www.aviationweather.gov/http://www.aviationweather.gov/

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Aviation Weather CenterAviation Weather Centerhttp://www.aviationweather.gov/flightpathhttp://www.aviationweather.gov/flightpath

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• Requires JavaRequires Java

• Therefore smartphones and Therefore smartphones and most tablets will not workmost tablets will not work

• Resizable mapResizable map

• Customizable contour intervalsCustomizable contour intervals



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The flight tool can help you The flight tool can help you avoid expected icing areas avoid expected icing areas along your route.along your route.

Example over AZ-NM from Tuesday, 24 February 2015.Example over AZ-NM from Tuesday, 24 February 2015.

*

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http://www.aviationweather.gov/icing/fip Current/forecast icing from AWC (Aviation Weather Center)

http://www.wrh.noaa.gov/zse/ Seattle CWSU home page, includes customizable map where you can add pireps, AIRMETs, CWAs, highest freezing level, radar, satellite, etc

http://www.wrh.noaa.gov/zse/icing_fcst.php Icing page from the Seattle CWSU, includes current/forecast icing graphics, highest freezing level current/forecast, link to AWC icing page

http://www.wrh.noaa.gov/zse/mobile.php Seattle CWSU mobile page includes Pacific NW links for radar, satellite, TAF/METARs, PIREPs, AIRMETs/SIGMETs, CWA/MIS, area hazards, other images, links to other NWS mobile pages

http://www.wrh.noaa.gov/zse/swipe.php Seattle CWSU "swipe" page, optimized for mobile devices, shows local radar, satellite, TAF/METARs, Vertical Wind Profile, local forecast, AIRMETs/SIGMETs, sunrise/sunset, local station plot map, local model text data

http://www.wrh.noaa.gov/zoa/MOBILE/ZOA2.htm Oakland CWSU mobile page has links including aviation text, hazards, radar, satellite, discussions, winds aloft, ADDS wind graphics, TAF/METAR, PIREPs, etc

http://mobile.weather.gov/ The NWS mobile page for basic local forecasts, radar, discussions, forecast graphics, etc

http://ruc.noaa.gov/soundings/ RAP (formerly RUC) vertical analyses and forecasts. These are Skew-T log-P soundings meteorologists use which display vertical moisture, temperature, winds, etc over a desired location.

http://www.aviationweather.gov/icing AWC icing page, including Icing SIGMETs, forecast icing, freezing levels, icing PIREPs, etc

http://www.aviationweather.gov/flightpath AWC Flight Path tool (requires Java) which can help a pilot determine the best path to avoid icing. It is customizable (both zooming into areas and showing what is along a specific path and altitude).

Links in the Presentation

Thank you forThank you foryour participation!your participation!

Further questions can be Further questions can be directed to the Center Weather directed to the Center Weather Service Unit inService Unit inAuburn, WashingtonAuburn, Washington

[email protected]@noaa.gov


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Documents

Aircraft Icing Jim Vasilj, Meteorologist Center Weather Service Unit Auburn, Washington NOAA/NWS Seattle Center Weather Service Unit (ZSE)