ICINGICING

Categories of IcingCategories 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 ConditionsNecessary 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 Supercooled Droplets – Why do they exist?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 SIGNIFICANTACCUMULATION

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 IcingClear 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 - CharacteristicsClear Icing - Characteristics

• Rapid accumulation– Droplets are large– Droplets are highly concentrated

• Smooth surface

• Hard

• Difficult to remove

FAVORABLE CONDITIONS

SMALL SUPERCOOLED DROPLETS IN STRATIFORM CLOUDS

TEMPERATURES 0°C TO -20°C

RIME ICING

Rime IcingRime 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 - CharacteristicsRime 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

FAVORABLE CONDITIONS

LARGE AND SMALL DROPLETS COEXIST

LIQUID AND FROZEN PARTICLES COEXIST

WET SNOW

MIXED ICING

FREEZING TEMPERATURES

Mixed IcingMixed 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 - CharacteristicsMixed 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 LocationsIcing 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

GROUND LEVEL

SEA LEVEL

1000

2000

3000

4000

5000

6000

7000

8000

9000

-20°C 0°C

MOST PROBABLE ICING LAYER

ICING LAYER

SINGLE FREEZING LEVEL

0°C

STRATUS CLOUDS

ICING ZONE

0°C 0°C

FAST ACCUMULATION

CUMULUS CLOUDS

OR LESS

OR LESS

TEMP 0°C OR LOWER

RAIN, DRIZZLE, OR WET SNOW

PRECIPITATION

WARM FRONTWARM AIR

MOIST AND STABLEABOVE FREEZING TEMPERATURES

STRATIFIED CLOUDS

FRONTS

COLD AIR

0°C

BELOW FREEZING TEMPERATURES

SUPERCOOLED RAIN FREEZES ON IMPACT

(FREEZING RAIN) {

WARM RAIN

RESPONSE ITEM

A PILOT FLYING AT 4,000 FEET REPORTS ICING CONDITIONS.BASED ON THE SOUNDING, TO AVOID THE ICING YOU WOULDADVISE 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 WOULDADVISE 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, ATWHAT ALTITUDE WOULD YOU EXPECT INITIAL ICING?

A. 3,000 FEET B. 5,000 FEET C. 7,000 FEET

DURING CLIMBOUT INTO THE CUMULIFORM CLOUD, ATWHAT ALTITUDE WOULD YOU EXPECT INITIAL ICING?

A. 3,000 FEET B. 5,000 FEET C. 7,000 FEET

7,000 FT

5,000 FT

3,000 FT

0oC

DefinitionsDefinitions

• 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.

DefinitionsDefinitions

• 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

DefinitionsDefinitions• 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.

DECREASESLIFTINCREASES

DRAG

DECREASESTHRUST

INCREASESWEIGHT

HAZARDOUS EFFECTS TO FLIGHTHAZARDOUS EFFECTS TO FLIGHT

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 Icing Forecasts Available from NWSNWS

Airmets

Sigmets

http://adds.aviationweather.gov/icing/

Other Aviation Weather ResourcesOther 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

The EndThe End