- Carburettor icing can happen at temperatures of up to 38 degrees Celsius.
- Carburettor heat should be applied immediately when an engine runs roughly.
Carburettor icing can occur even in relatively warm conditions - the higher the humidity, the more likely it is that ice will form in the air-intake system.
Carburettor icing likely contributed to an accident on 14 July 2015, when the pilot of a Robinson R44 helicopter was conducting aerial mustering operations on a property near Alice Springs.
The pilot felt a small vibration, and initially thought it was due to loose tape on the main rotor blade. The pilot looked for a suitable landing site, but the vibration increased significantly.
Carburettor icing can happen at temperatures of up to 38 degrees Celsius – it is less likely at very cold temperatures.
As the helicopter descended, the pilot maneuvered it through a gap between trees, and pushed the cyclic forward to maintain airspeed. The pilot lowered the collective and noticed the engine seemed to go very quiet. The low rotor revolutions per minute warning horn sounded. The pilot made a radio call to advise another pilot operating nearby that the helicopter was going down. The pilot then flared the helicopter to try to cushion the landing impact. The right skid touched down first, and the helicopter rolled onto its right side.
The pilot sustained minor injuries, and the helicopter was substantially damaged. The weather was fine with no visible signs of moisture and the pilot did not turn the carburettor heat on at any stage during the flight.
According to the Carburettor Icing Probability chart, current conditions indicated a high probability of serious carburettor icing at descent power. At the time it was 12 degrees Celsius with relatively high humidity of 40 – 45 per cent.
The icy facts:
- Carburettors cause evaporation, which cools the air.
- Carburettor icing can happen at temperatures of up to 38 degrees Celsius – it is less likely at very cold temperatures.
- Carburettor icing is more likely at partial power settings because of the cooling effect of a partly closed throttle butterfly.
Safety message
Carburettor heat should be applied immediately when an engine runs roughly.
Apply carburettor heat immediately as per the emergency checklist in the approved operating handbook or aircraft flight manual for your aircraft type.
Use this CASA probability chart to work out the risk of carburettor icing prior to each flight.
Read the report: Collision with terrain involving a Robinson R44, VH-VOH, 130 km east of Alice Springs, Northern Territory, on 14 July 2015
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