Aircraft Icing Conditions
Understanding ice types, hazards, and survival strategies
Why Icing Matters
Ice accumulation degrades aircraft performance in multiple ways: it adds weight, disrupts the smooth airflow over wings and tail surfaces destroying lift, blocks pitot tubes and static ports, restricts engine air intake, and can freeze control surfaces. The effects compound—a little ice makes the aircraft work harder, which may require more power, which may lead to more time in icing conditions.
Accidents caused by icing often result from pilots either not recognizing they're in icing conditions, underestimating how fast ice accumulates, or lacking a viable escape plan. This guide covers the knowledge you need to fly safely in cold weather.
Types of Structural Icing
Clear Ice (Glaze Ice)
Forms when large supercooled water droplets strike the aircraft and flow back before freezing. Creates smooth, transparent ice that's hard to see and very difficult to remove. Most dangerous type.
Rime Ice
Forms when small supercooled droplets freeze instantly on impact, trapping air bubbles. Creates rough, opaque white ice. Easier to see and generally easier to remove than clear ice, but still dangerous.
Mixed Ice
Combination of clear and rime ice, often with a rough, uneven surface. Forms when droplet sizes vary or temperature fluctuates. Has properties of both types and can be particularly disruptive to airflow.
Icing Temperature Range
icing zone Rime ice
predominates Ice unlikely
(too cold)
Key insight: Below about -40°C, water droplets are usually already frozen as ice crystals, which generally bounce off the aircraft rather than sticking. The most dangerous temperatures are near freezing where supercooled liquid water is most common.
Carburetor and Induction Icing
Carburetor Ice - The Hidden Threat
Unlike structural icing, carburetor ice can form on warm, humid days. The pressure drop in the carburetor venturi can cool air by 30°C (70°F) or more, turning invisible water vapor into ice that blocks airflow.
Warning Signs
- • Gradual RPM decrease (fixed-pitch prop)
- • Manifold pressure decrease (constant-speed)
- • Rough engine operation
- • Engine may quit without warning
Prevention
- • Apply carb heat before power reduction
- • Use carb heat on approach/descent
- • Monitor for symptoms continuously
- • When in doubt, apply heat
Carb ice is most likely at temperatures between -7°C and +21°C with visible moisture or relative humidity above 50%. The classic accident scenario is a pilot reducing power for descent on a humid day and having the engine quit on short final.
Icing in Weather Products
AIRMETs and SIGMETs
AIRMET ZULU UPDT 2 FOR ICE AND FRZLVL VALID UNTIL 162100
FROM SEA TO GEG TO MLP TO PDX TO SEA
MOD ICE BTN FRZLVL AND FL180. FRZLVL 060-080.
This AIRMET Zulu warns of moderate icing between the freezing level (6,000-8,000 ft) and FL180 in the Pacific Northwest. Non-FIKI aircraft should avoid these altitudes.
PIREPs - Your Best Source
SEA UA /OV SEA090020/TM 1545/FL085/TP C172/IC LGT-MOD RIME 070-090
A Cessna 172 reported light to moderate rime icing between 7,000 and 9,000 feet, 20 miles east of Seattle at 15:45Z. PIREPs give you real-time, specific information that forecasts cannot match.
Always File Icing PIREPs
If you encounter icing—or if forecasted icing doesn't materialize—file a PIREP. Include altitude, temperature, ice type, and intensity. Your report could save another pilot's life.
Escape Strategies
If you inadvertently enter icing conditions, you need an immediate plan. Every second in ice degrades your aircraft further.
↑ Climb Above
If performance permits, climb above the clouds to colder air where icing is less likely. Requires knowing cloud tops.
Best when: Tops are low, aircraft has climb performance margin
↓ Descend Below
Descend to warmer air below freezing level. Ice will shed as temperature rises above 0°C. Mind terrain.
Best when: Above freezing level, terrain permits, bases are above minimums
← Turn Back
180° turn to exit the icing area. You know conditions behind you were survivable.
Best when: Icing just started, you haven't gone far into the area
⟲ Divert and Land
Land at the nearest suitable airport. Don't try to continue to destination while accumulating ice.
Best when: Significant ice accumulated, performance degraded
Critical: Have an Escape Plan BEFORE Entry
Before flying in potential icing conditions, know: Where is the freezing level? What are cloud tops and bases? Where can I divert? What's the minimum safe altitude for terrain? Don't enter potential icing without answers to these questions.
Key Takeaways
- Icing requires visible moisture AND temperatures between +2°C and -20°C
- Clear ice is most dangerous—heavy, hard to see, difficult to remove
- Carb ice can form on warm, humid days—use carb heat proactively
- Non-FIKI aircraft must not fly into known icing conditions
- Have an escape plan before entering potential icing—climb, descend, turn, or land