2 Categories of Icing Structural Icing Induction Icing Instrument Icing Forms on the surface of the airframeInduction IcingForms in air intakes of enginesInstrument IcingForms on pitot tube and other exterior instruments
3 Necessary Conditions Temperature of 0 Celsius or colder Supercooled liquid dropletsLiquid cloud or precipitation droplets at below freezing temperaturesWet snowflakesSnowflakes at temperatures near 0CMixture 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 -10CIce Condensation Nuclei levels are present at 50% between -10C and -14CIce Condensation Nuclei are present nearly to 100% by -20CSeveral 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 FLIGHTSEVERE - RAPID, DANGEROUS ACCUMULATIONS
6 CLEAR ICING FAVORABLE CONDITIONS LARGE DROPLETS IN CUMULIFORM CLOUDS OR FREEZING RAINTEMPERATURES 0°C TO -20°C
7 Clear Icing Clear appearance (glaze) Associated with strong upward motionFavorable conditionsLarge dropletsCumuliform cloudsFreezing rainTemperatures 0 to -10 C (sometimes down to -20 C)Formation ProcessSupercooled droplets impact, flow, conform, and then freeze on the aircraft surface.
8 Clear Icing - Characteristics Rapid accumulationDroplets are largeDroplets are highly concentratedSmooth surfaceHardDifficult to remove
10 RIME ICING FAVORABLE CONDITIONS SMALL SUPERCOOLED DROPLETS IN STRATIFORM CLOUDSTEMPERATURES 0°C TO -20°C
11 Rime Icing White, frosty appearance Favorable conditions Small water dropletsStratiform cloudsTemperatures 0 to -20 CFormation ProcessDroplets freeze on impactAir is trapped between frozen particles
12 Rime Icing - Characteristics Accumulates more slowly than clear icingDroplets are smallerDroplets are less concentratedIrregular, pebble-like surfaceStructurally weaker than clear icingEffect of trapped air
15 MIXED ICING FAVORABLE CONDITIONS LARGE AND SMALL DROPLETS COEXIST LIQUID AND FROZEN PARTICLES COEXISTWET SNOWFREEZING TEMPERATURES
16 Mixed Icing Glossy white appearance Associated with strong upward motionFavorable conditionsLarge and small droplets coexistLiquid and frozen particles coexistWet snowFreezing temperatures (Often much colder than -10C)Formation ProcessCombines clear and rime icing processes and/or wet snowflakes
17 Mixed Icing - Characteristics Rapid accumulationParticles are largeParticles are highly concentratedRough surfaceCreates turbulent flow over wingMost effective in reducing aerodynamic efficiency (turbulent flow over wing reduces lift)Difficult to remove
19 RESPONSE ITEMWHAT INTENSITY OF ICING IDENTIFIES SIGNIFICANT ACCUMULATIONS AFTER RELATIVELY SHORT PERIODS OF FLIGHT?A. LIGHTB. MODERATEC. SEVEREA. LIGHTB. MODERATEC. SEVERE
20 RESPONSE ITEMSOLID, SMOOTH ICE FORMED EITHER FROM SUPERCOOLED WATER DROPS OR FROM FREEZING RAIN IS CALLED ________ ICE.A. CLEARB. RIMEC. MIXEDA. CLEARB. RIMEC. MIXED
21 RESPONSE ITEMTHE TYPE OF ICING USUALLY ASSOCIATED WITH STRATIFORM CLOUDS ISA. CLEAR.B. RIME.C. MIXED.A. CLEAR.B. RIME.C. MIXED.
22 Icing LocationsIcing locations are layer and positions in the atmosphere with icing potentialDetermined by temperatures, generally in the range of 0 to -20CTemperatures statistically most favorable for supercooled droplets
26 CUMULUS CLOUDSFAST ACCUMULATION0°C0°COR LESSOR LESS
27 RAIN, DRIZZLE, OR WET SNOW PRECIPITATIONRAIN, DRIZZLE, OR WET SNOWTEMP 0°C OR LOWER
28 0°C FRONTS WARM RAIN WARM AIR COLD AIR BELOW FREEZING TEMPERATURES STRATIFIED CLOUDSWARM AIRABOVE FREEZING TEMPERATURESWARM FRONTMOIST AND STABLEWARM RAINCOLD AIRBELOW FREEZING TEMPERATURESSUPERCOOLED RAIN FREEZES ON IMPACT (FREEZING RAIN)
29 RESPONSE ITEM A PILOT FLYING AT 4,000 FEET REPORTS ICING CONDITIONS. BASED ON THE SOUNDING, TO AVOID THE ICING YOU WOULDADVISE THE PILOT TOA. 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 WOULDADVISE THE PILOT TOA. CLIMB TO 5,000 FEET.B. DESCEND TO 3,000 FEET.C. CLIMB ABOVE 8,000 FEET.
30 RESPONSE ITEM DURING CLIMBOUT INTO THE CUMULIFORM CLOUD, AT 7,000 FT5,000 FT0oC3,000 FTDURING CLIMBOUT INTO THE CUMULIFORM CLOUD, ATWHAT ALTITUDE WOULD YOU EXPECT INITIAL ICING?A. 3,000 FEETB. 5,000 FEETC. 7,000 FEETDURING CLIMBOUT INTO THE CUMULIFORM CLOUD, ATWHAT ALTITUDE WOULD YOU EXPECT INITIAL ICING?A. 3,000 FEETB. 5,000 FEETC. 7,000 FEET
31 Definitions Frost – Deposition of ice crystals from water vapor Must have temperatures at or below freezing with a high relative humidityCold 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.
33 DefinitionsFog – 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 humidityFreezing Fog (FZBR or FZFG) – The development of fog at temperatures below freezingCauses deposition of ice onto exposed surfaces
35 DefinitionsSleet (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.
37 HAZARDOUS EFFECTS TO FLIGHT DECREASESLIFTINCREASESDRAGDECREASESTHRUSTINCREASESWEIGHT
38 ICING INTENSITY EFFECTS (WITHOUT DEICERS/WITH DEICERS) TRACE - NO HAZARDS/ NO DEICERS REQUIREDLIGHT - HAZARDOUS IF CONTINUED/ OCCASIONAL USE OF DEICERS REQUIREDMODERATE - HAZARDOUS, REQUIRES DIVERSION/CONTINUOUS USE OF DEICERS REQUIREDSEVERE - IMMEDIATE HAZARD/ UNCONTROLLED BY DEICERS
39 RESPONSE ITEMTHE ICING INTENSITY THAT REQUIRES CONTINUOUS USE OF DEICERS ISA. LIGHT.B. MODERATE.C. SEVERE.THE ICING INTENSITY THAT REQUIRES CONTINUOUS USE OF DEICERS ISA. LIGHT.B. MODERATE.C. SEVERE.
40 OBSERVED REPORTS OF ICING CONDITIONS METAR KORD Z 12010KT 5SM PL BR OVC008 M11/M13 A3045 RMK SLP315METAR KOMA Z 09015KT 7SM FZRA OVC010 M07/M09 A3040 RMK SLP300UA/OV KTUL225050/TM 2335/FL080/TP PA28/ SK OVC025-TOP060/TA M06/IC LGT RIME /RM FRZLVL 045 DURC
41 Icing Forecasts Available from NWS AirmetsSigmets