The ATSB has investigated several occurrences of reported partial power loss situations where carburettor icing was suspected.
On 10 June 2012, a Robinson Helicopter Company R44 Raven 1 was seriously damaged following a reported loss of power and collision with terrain near Maryvale in the Northern Territory.
The helicopter was providing support and aerial filming of a competitor participating in the annual Finke Desert race with a pilot and three passengers on board.
The helicopter impacted the ground in a level attitude collapsing the skids on impact. One passenger was seriously injured in the accident.
The ATSB could not determine a definitive reason for the reported loss of engine power, however, a review of the carburettor icing probability chart revealed that the temperature/dew point spread, put the flight in the ‘serious icing – descent power’ operating realm.
When an aircraft is fitted with a carburettor air temperature gauge, carburettor heat is applied to a level to maintain the temperature outside the caution range. The carburettor heat assist system fitted to the Robinson R44 Raven 1 is designed to automatically apply a level of heat corresponding to the amount of power being applied. It does not directly sense carburettor air temperature and further adjustments may be required to be made by the pilot to maintain the temperature outside the caution range.
Robinson Helicopter Company has previously issued advice about the use of the carburettor heat assistance system, warning that if used it will reduce carburettor heat on lift off and may require adjustment in flight.
The ATSB encourages operators and pilots to learn more about the dangers and methods of preventing carburettor icing.
You can find this and other investigations in the ATSB’s Aviation Short Investigation Bulletin. The bulletin highlights valuable safety lessons for pilots, operators and safety managers.Last update 04 January 2013