What happened
On 21 February 2009, a Mickleburgh L107, registration G-BZVC, departed Fenland Airfield for a flight to Tibenham. Shortly after takeoff, while at an altitude between 400 and 700 feet, the aircraft entered a steep left turn. The pilot issued a MAYDAY call, expressing an intention to land back at the airfield, though no specific technical difficulties were reported.
During the turn onto the final approach for Runway 36, the aircraft flew through the extended centerline, stalled, and entered a spin. After several turns, the aircraft struck the ground in a field near the airfield. The pilot sustained one fatal injury upon impact. The aircraft was destroyed.
The investigation
The AAIB examined the wreckage and the engine systems. Investigators found that the propeller was not rotating at the time of impact and the fuel tank was empty due to rupture during the crash.
Technical scrutiny of the engine revealed a malfunction in the carburettor hot air system. The movable flap within the hot/cold air box was found to be sticking in the cold air position because it was catching against the lower channel of the unit. This interference had caused the lever arm to become loose over time. Meteorological data for the morning of the accident indicated conditions highly conducive to serious carburettor icing at any power setting.
Findings
- The accident was likely prompted by a partial loss of engine power caused by the failure of the carburettor heat system in icing-prone conditions.
- The aircraft entered a spin during a low-speed turn on final approach.
- The pilot's decision to return to the airfield may have been influenced by concerns regarding the suitability of the surrounding waterlogged fields for a forced landing.
- The mechanical failure of the carburettor heat flap was caused by physical interference within the air box assembly.