What happened
On 13 March 1999, a Cessna F150L, registration G-AYRF, was conducting a private cross-country flight as part of a student pilot's training for a Private Pilot's Leicense. While approaching Shobden at approximately 3,000 feet, the pilot contacted the airfield and was instructed to join the overhead pattern at 2,000 feet.
In preparation for the descent, the pilot applied carburettor heat and reduced power to 1,700 RPM. Upon reaching the target altitude of 2,000 feet, the pilot deselected the carburettor heat and increased the throttle. At this moment, the engine failed to respond to the power increase. The pilot immediately began searching for a suitable landing site while checking engine instruments and control settings. During this process, the engine ceased running entirely. After failing to restart the engine, the pilot issued a MAYDAY call and prepared for a forced landing in a field.
Due to the presence of trees surrounding the available landing area, the pilot was forced to land halfway down the available runway. The ground was notably wet, and as the aircraft touched down, the nosewheel sank into the soft surface and collapsed. The aircraft eventually came to a halt after striking a ditch at the edge of the field, resulting in substantial damage to the airframe and landing gear. There were no injuries to the pilot.
The investigation
Investigators examined the aircraft and the circumstances surrounding the engine failure. A post-accident engineering inspection was conducted, but it did not identify a definitive mechanical fault or obvious cause for the engine's loss of power. The investigation also considered the pilot's actions regarding engine management during the descent.
Findings
- The engine failed to respond to throttle input immediately after the pilot removed the carburettor heat.
- Carburettor icing was identified as the most likely cause of the engine failure.
- It is believed the pilot may not have maintained the carburettor heat in the 'HOT' position for a sufficient duration to clear any ice buildup before reducing power and subsequently deselecting the heat.