Icing

Icing refers to the accretion of ice on the airframe or engine of an aircraft in flight, resulting from the freezing of supercooled water droplets on contact with cold aircraft surfaces. Airframe icing is one of the most serious hazards in aviation — it degrades lift, increases drag, adds weight, and can render flight controls inoperative.

Types of In-Flight Icing

  • Clear ice (glaze ice): Forms in freezing rain or large supercooled droplets; dense, hard, smooth; worst structural icing — most difficult to remove and adheres strongly to surfaces
  • Rime ice: Forms in small supercooled droplets (stratiform cloud); white, opaque, rough; less dense than clear ice; can be shed more easily by de-icing systems
  • Mixed ice: Combination of clear and rime; common in convective clouds with varying drop sizes

Where Icing Occurs

  • In cloud at temperatures between 0°C and approximately −40°C (below −40°C, water crystallizes and does not supercool)
  • In freezing precipitation (FZRA, FZDZ) — potentially the most severe icing
  • In freezing fog
  • Above or near thunderstorms (large supercooled droplets at high altitude)
  • In mountain wave cloud (intense lift creates abundant supercooled water)

Effect on Aircraft Performance

  • Lift reduced — ice changes wing profile and increases stall speed
  • Drag significantly increased — rough ice surface, disrupted airflow
  • Weight added — ice accumulation can be substantial (hundreds of kilograms on large aircraft)
  • Propeller efficiency reduced — asymmetric shedding causes vibration
  • Pitot-static icing can cause erroneous instrument readings
  • Carburettor icing (separate phenomenon) can cause engine power loss at temperatures well above 0°C

De-icing vs. Anti-icing

  • De-icing: Removes ice that has already formed (inflatable boots, hot air, heated surfaces, fluid)
  • Anti-icing: Prevents ice from forming (bleed air, electrothermal heat, TKS fluid)
  • Most light aircraft are NOT certified for flight into known icing (FIKI) — check the AFM/POH carefully

On the TC Written Exam

Icing is heavily tested in both PPL and CPL meteorology sections. Know the types, where icing occurs, how it affects performance, and the regulatory prohibition against flight into known icing conditions without FIKI certification.

Related Terms

See also: Freezing Rain, Freezing Drizzle, Ice Pellets, Aircraft Critical Surface Contamination, SIGMET.