Icing can be extremely hazardous to aircraft. It is a cause factor in a number of aircraft accidents each year. Often aircraft are required to operate in environmental conditions where the probability of aircraft structural icing is high. A large number of aircraft, including the Aerosonde, are currently not fitted with appropriate de-icing equipment to fly safely in known icing conditions. Even with appropriate de-icing instrumentation, all aircraft should avoid potential severe, or extreme, icing conditions. As the Aerosonde is a small aircraft even small amounts of ice accumulation may be extremely detrimental to the aircraft.
The need for an Aerosonde in-flight airframe icing nowcast scheme became obvious after the loss of two Aerosonde aircraft in 1999, due to structural airframe icing, during operations in the harsh environmental conditions of Barrow, Alaska. Development of an Aerosonde in-flight icing model began soon after. The current Aerosonde in-flight icing model incorporates several of the temperature and humidity thresholds used in various other mesoscale T-RH icing schemes. It should be noted that this icing scheme does not address the problem of carburettor icing, only providing information on atmospheric conditions that have the potential to cause the accumulation of ice on the surface of an aircraft. This icing scheme will provide a useful tool to Aerosonde controllers - nowcasting the 'danger' areas for aircraft (regions in which to avoid). The Aerosonde in-flight icing scheme, along with Aerosonde observations and icing sensor data will be presented in this paper.