What happened
On 16 September 2007, a Piper PA-28-140 Cherokee, registration G-AVGD, was conducting a training flight from Cranfield to Deanland Airfield. The flight was intended to familiarise a recently requalified pilot with the aircraft's navigation equipment.
While the aircraft was on the base leg of the landing circuit, the engine failed to respond to throttle inputs. Despite the instructor taking control, switching fuel tanks, and activating the electric fuel pump, the engine remained unresponsive even after the carburettor heat was applied. The instructor declared a ‘MAYDAY’ and executed a forced landing in a field approximately 750 metres northeast of the runway. During the landing, the aircraft struck a hedge, causing the wings to separate from the fuselage. Both the pilot and the passenger sustained minor injuries and were able to exit the wreckage without assistance.
The investigation
The investigation focused on the engine's failure to respond to power increases. It was noted that the aircraft had undergone repairs following a previous accident in 2006, which included the replacement of a control cable.
Investigators found that the carburettor heat control protruded from the instrument panel by more than 25 mm when in the cold position. Although this issue had been previously noted by the engineering organisation, it had not been corrected. This protrusion prevented the control from reaching its full travel, which in turn restricted the air valve from reaching the fully hot position. This limitation hindered the pilot's ability to effectively manage ice formation or removal within the carburettor.
Findings
- The engine failure was likely caused by carburettor icing.
- Atmospheric conditions, with a temperature of +15ºC and a dew point of +11ºC, were known to be conducive to icing during cruise and descent.
- The carburettor heat control was improperly positioned, protruding over 25 mm from the panel.
- The mechanical misalignment prevented the air valve from reaching the necessary position to fully mitigate icing.