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ICING

ICING. Categories of Icing. Structural Icing Forms on the surface of the airframe Induction Icing Forms in air intakes of engines Instrument Icing Forms on pitot tube and other exterior instruments. Necessary Conditions. Temperature of 0 Celsius or colder Supercooled liquid droplets

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ICING

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  1. ICING

  2. Categories of Icing • Structural Icing • Forms on the surface of the airframe • Induction Icing • Forms in air intakes of engines • Instrument Icing • Forms on pitot tube and other exterior instruments

  3. Necessary Conditions • Temperature of 0 Celsius or colder • Supercooled liquid droplets • Liquid cloud or precipitation droplets at below freezing temperatures • Wet snowflakes • Snowflakes at temperatures near 0C • Mixture of ice particles and supercooled water droplets

  4. Supercooled Droplets – Why do they exist? • Ice Condensation Nuclei typically do not exist at temperatures warmer than -10C • Ice Condensation Nuclei levels are present at 50% between -10C and -14C • Ice Condensation Nuclei are present nearly to 100% by -20C • Several types of clay particles are common ice nuclei, silver iodide is another.

  5. ICING INTENSITIES TRACE - PERCEPTIBLE, NO SIGNIFICANT ACCUMULATION LIGHT - SIGNIFICANT ACCUMULATION FOR A PROLONGED FLIGHT (OVER 1 HOUR) MODERATE - SIGNIFICANT ACCUMULATION FOR SHORTER PERIODS OF FLIGHT SEVERE - RAPID, DANGEROUS ACCUMULATIONS

  6. CLEAR ICING FAVORABLE CONDITIONS LARGE DROPLETS IN CUMULIFORM CLOUDS OR FREEZING RAIN TEMPERATURES 0°C TO -20°C

  7. Clear Icing • Clear appearance (glaze) • Associated with strong upward motion • Favorable conditions • Large droplets • Cumuliform clouds • Freezing rain • Temperatures 0 to -10 C (sometimes down to -20 C) • Formation Process • Supercooled droplets impact, flow, conform, and then freeze on the aircraft surface.

  8. Clear Icing - Characteristics • Rapid accumulation • Droplets are large • Droplets are highly concentrated • Smooth surface • Hard • Difficult to remove

  9. RIME ICING FAVORABLE CONDITIONS SMALL SUPERCOOLED DROPLETS IN STRATIFORM CLOUDS TEMPERATURES 0°C TO -20°C

  10. Rime Icing • White, frosty appearance • Favorable conditions • Small water droplets • Stratiform clouds • Temperatures 0 to -20 C • Formation Process • Droplets freeze on impact • Air is trapped between frozen particles

  11. Rime Icing - Characteristics • Accumulates more slowly than clear icing • Droplets are smaller • Droplets are less concentrated • Irregular, pebble-like surface • Structurally weaker than clear icing • Effect of trapped air

  12. MIXED ICING FAVORABLE CONDITIONS LARGE AND SMALL DROPLETS COEXIST LIQUID AND FROZEN PARTICLES COEXIST WET SNOW FREEZING TEMPERATURES

  13. Mixed Icing • Glossy white appearance • Associated with strong upward motion • Favorable conditions • Large and small droplets coexist • Liquid and frozen particles coexist • Wet snow • Freezing temperatures (Often much colder than -10C) • Formation Process • Combines clear and rime icing processes and/or wet snowflakes

  14. Mixed Icing - Characteristics • Rapid accumulation • Particles are large • Particles are highly concentrated • Rough surface • Creates turbulent flow over wing • Most effective in reducing aerodynamic efficiency (turbulent flow over wing reduces lift) • Difficult to remove

  15. RESPONSE ITEM WHAT INTENSITY OF ICING IDENTIFIES SIGNIFICANT ACCUMULATIONS AFTER RELATIVELY SHORT PERIODS OF FLIGHT? A. LIGHT B. MODERATE C. SEVERE A. LIGHT B. MODERATE C. SEVERE

  16. RESPONSE ITEM SOLID, SMOOTH ICE FORMED EITHER FROM SUPERCOOLED WATER DROPS OR FROM FREEZING RAIN IS CALLED ________ ICE. A. CLEAR B. RIME C. MIXED A. CLEAR B. RIME C. MIXED

  17. RESPONSE ITEM THE TYPE OF ICING USUALLY ASSOCIATED WITH STRATIFORM CLOUDS IS A. CLEAR. B. RIME. C. MIXED. A. CLEAR. B. RIME. C. MIXED.

  18. Icing Locations • Icing locations are layer and positions in the atmosphere with icing potential • Determined by temperatures, generally in the range of 0 to -20C • Temperatures statistically most favorable for supercooled droplets

  19. 9000 8000 7000 6000 5000 4000 3000 2000 GROUND LEVEL 1000 SEA LEVEL ICING LAYER SINGLE FREEZING LEVEL MOST PROBABLE ICING LAYER -20°C 0°C

  20. STRATUS CLOUDS ICING ZONE 0°C

  21. CUMULUS CLOUDS FAST ACCUMULATION 0°C 0°C OR LESS OR LESS

  22. PRECIPITATION RAIN, DRIZZLE, OR WET SNOW TEMP 0°C OR LOWER

  23. FRONTS 0°C • STRATIFIED CLOUDS WARM AIR ABOVE FREEZING TEMPERATURES WARM FRONT MOIST AND STABLE WARM RAIN COLD AIR BELOW FREEZING TEMPERATURES SUPERCOOLED RAIN FREEZES ON IMPACT (FREEZING RAIN)

  24. RESPONSE ITEM A PILOT FLYING AT 4,000 FEET REPORTS ICING CONDITIONS. BASED ON THE SOUNDING, TO AVOID THE ICING YOU WOULD ADVISE THE PILOT TO A. CLIMB TO 5,000 FEET. B. DESCEND TO 3,000 FEET. C. CLIMB ABOVE 8,000 FEET. A PILOT FLYING AT 4,000 FEET REPORTS ICING CONDITIONS. BASED ON THE SOUNDING, TO AVOID THE ICING YOU WOULD ADVISE THE PILOT TO A. CLIMB TO 5,000 FEET. B. DESCEND TO 3,000 FEET. C. CLIMB ABOVE 8,000 FEET.

  25. RESPONSE ITEM 7,000 FT 0oC 5,000 FT 3,000 FT DURING CLIMBOUT INTO THE CUMULIFORM CLOUD, AT WHAT ALTITUDE WOULD YOU EXPECT INITIAL ICING? A. 3,000 FEET B. 5,000 FEET C. 7,000 FEET DURING CLIMBOUT INTO THE CUMULIFORM CLOUD, AT WHAT ALTITUDE WOULD YOU EXPECT INITIAL ICING? A. 3,000 FEET B. 5,000 FEET C. 7,000 FEET

  26. Definitions • Frost – Deposition of ice crystals from water vapor • Must have temperatures at or below freezing with a high relative humidity • Cold Soak – Occurs when an aircraft flies from a region of very cold temperatures to a region of warmer temperatures with high humidity, causing atmospheric moisture to deposit into ice crystals onto the aircraft.

  27. Definitions • Fog – Condensation of water vapor into cloud droplets near the ground (cloud on the ground) • BR (3/4SM or Greater) • FG (1/2SM or Lower) • Light winds, clear skies and high low level humidity • Freezing Fog (FZBR or FZFG) – The development of fog at temperatures below freezing • Causes deposition of ice onto exposed surfaces

  28. Definitions • Sleet (PL) – Snow that partially melts in the atmosphere then refreezes into a small ice pellet by the time it reaches the ground. • Hail (GR) – Ice particles that get suspended in a thunderstorm and fall to the ground once the thunderstorm updraft can no longer sustain its weight. • Freezing Rain (FZRA) – Rain that falls into a shallow layer of subfreezing air near the ground and freezes on contact with surfaces on or near the ground.

  29. HAZARDOUS EFFECTS TO FLIGHT DECREASES LIFT INCREASES DRAG DECREASES THRUST INCREASES WEIGHT

  30. ICING INTENSITY EFFECTS (WITHOUT DEICERS/WITH DEICERS) TRACE - NO HAZARDS/ NO DEICERS REQUIRED LIGHT - HAZARDOUS IF CONTINUED/ OCCASIONAL USE OF DEICERS REQUIRED MODERATE - HAZARDOUS, REQUIRES DIVERSION/CONTINUOUS USE OF DEICERS REQUIRED SEVERE - IMMEDIATE HAZARD/ UNCONTROLLED BY DEICERS

  31. RESPONSE ITEM THE ICING INTENSITY THAT REQUIRES CONTINUOUS USE OF DEICERS IS A. LIGHT. B. MODERATE. C. SEVERE. THE ICING INTENSITY THAT REQUIRES CONTINUOUS USE OF DEICERS IS A. LIGHT. B. MODERATE. C. SEVERE.

  32. OBSERVED REPORTS OF ICING CONDITIONS METAR KORD 152355Z 12010KT 5SM PL BR OVC008 M11/M13 A3045 RMK SLP315 METAR KOMA 092355Z 09015KT 7SM FZRA OVC010 M07/M09 A3040 RMK SLP300 UA/OV KTUL225050/TM 2335/FL080/TP PA28/ SK OVC025-TOP060/TA M06/IC LGT RIME 045-060/RM FRZLVL 045 DURC

  33. Icing Forecasts Available from NWS Airmets Sigmets http://adds.aviationweather.gov/icing/

  34. Other Aviation Weather Resources • National Weather Service • www.nws.noaa.gov or www.weather.gov • National Weather Service Detroit/Pontiac • www.crh.noaa.gov/dtx or www.weather.gov/detroit • NWS Detroit/Pontiac Area Forecast Discussions • www.crh.noaa.gov/dtx/wxnow/sfd_index.php • Aviation Weather Center • http://aviationweather.gov • The Front Publication • Http://aviationweather.gov/general/pubs/front

  35. The End

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