1. ICING

2. 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

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

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

11. 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

12. 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

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

16. 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

17. 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

19. 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

20. 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

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

22. 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

23. 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

25. STRATUS CLOUDS
ICING ZONE
0°C

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

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

28. 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)

29. 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.

30. 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

31. 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.

33. 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

35. 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.

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

38. 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

39. 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.

40. OBSERVED REPORTS OF ICING CONDITIONS
METAR KORD Z 12010KT 5SM PL BR OVC008 M11/M13 A3045 RMK SLP315
METAR KOMA Z 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 /RM FRZLVL 045 DURC

41. Icing Forecasts Available from NWS
Airmets
Sigmets

49. Other Aviation Weather Resources
National Weather Service or
National Weather Service Detroit/Pontiac or
NWS Detroit/Pontiac Area Forecast Discussions
Aviation Weather Center
The Front Publication

50. The End