What happened
On 15 December 2019, a Colibri MB2, registration G-BUDW, departed from a grass airstrip near Mavis Enderby, Lincolnshire, for a short flight intended to test a recently modified fuel system. Witnesses observed the aircraft climbing after takeoff, noting that while the engine initially sounded smooth, it soon began to sputter and lose power. As the aircraft passed over a nearby hangar, the engine sound changed to a 'fizzing and popping' noise, and the aircraft failed to maintain its climb.
The aircraft subsequently disappeared from view. A search of the area conducted by another pilot revealed the wreckage approximately 50 metres north of the runway. The impact, which occurred while the aircraft was likely attempting to fly a circuit to return to the airfield, resulted in the death of the pilot. The aircraft was destroyed upon impact with the soft, clay soil.
The investigation
AAIB investigators examined the wreckage and the engine, finding the powerplant to be in a state of significant disrepair. The investigation focused on the engine's mechanical condition, the recent modifications made to the fuel system, and the pilot's maintenance practices.
Examination of the engine revealed several critical defects. A crack was identified in the cylinder head of cylinder 2, and a split was found in the inlet manifold joint. Furthermore, the investigation found that carbon and oil deposits had accumulated on the valve seats, with some flakes of debris becoming trapped, which prevented the valves from sealing properly. The investigation also noted that the pilot had recently altered the fuel system configuration without documented approval from LAA Engineering.
Findings
- The engine was in poor mechanical condition, characterized by a crack in the cylinder head and a split in the induction manifold.
- Significant loss of compression was present in multiple cylinders due to valve seat issues and debris.
- The engine experienced a partial power loss during the climb, which likely led the pilot to attempt a return to the runway, ultimately resulting in the impact.
- There was no evidence of a formal maintenance schedule or regular engine health monitoring, such as tracking compression trends or oil consumption.
- Modifications to the fuel system had been implemented without the required LAA Engineering approval process.