ICING

Categories of Icing Structural Icing Induction Icing Instrument 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 Liquid cloud or precipitation droplets at below freezing temperatures Wet snowflakes Snowflakes at temperatures near 0C Mixture of ice particles and supercooled water droplets

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.

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

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

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.

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

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

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

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

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

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

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

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

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

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

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

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

STRATUS CLOUDS ICING ZONE 0°C

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

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

0°C FRONTS WARM RAIN WARM AIR COLD AIR BELOW FREEZING TEMPERATURES 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)

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.

RESPONSE ITEM DURING CLIMBOUT INTO THE CUMULIFORM CLOUD, AT 7,000 FT 5,000 FT 0oC 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

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.

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

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.

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

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

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.

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

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

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

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