8.28 Aircraft Icing

8.28.2 List the hazards of airframe icing to aircraft in flight.

Airframe icing is hazardous because it changes the shape, weight and performance of the aircraft.

The main hazards are:

• Reduced lift due to distortion of the aerofoil shape.
• Increased drag caused by the rough ice-covered surfaces.
• Increased weight due to ice accumulation.
• Increased stalling speed due to increased weight and reduced lift.
• Reduced controllability because airflow over control surfaces may be disrupted.
• Reduced aircraft performance, including reduced climb rate and increased power required.
• Blocked pitot/static system, causing unreliable airspeed, altitude or vertical speed indications.
• Reduced forward visibility if ice forms on the windscreen.
• Vibration or imbalance if ice forms unevenly on propellers, rotors or airframe surfaces.
• Interference with aerials, vents, controls or moving surfaces.

Even a small amount of ice can significantly affect the performance and handling of a light aircraft.

8.28.4 Explain the processes involved in the formation of hoar frost on an aircraft on the ground and in flight.

Hoar frost forms when water vapour changes directly into ice on a surface that is below freezing.