What happened
On 21 August 2018, a Morane Saulnier Rallye 150ST, registration G-BDWH, departed Pymore Farm airstrip for a flight to Dunkeswell Airfield. Shortly after takeoff, while climbing to approximately 1,200 ft, smoke began entering the cockpit from beneath the instrument panel. The pilot opened the canopy to vent the smoke, but the engine subsequently stopped, though the propeller continued to windmill.
In an attempt to manage the situation, the pilot switched off the electrical master switch and adjusted the fuel selector. The aircraft was flying over undulating terrain consisting of small fields and woodland. The pilot attempted to land in a selected field but was unable to clear a nearby solar farm, resulting in an overshoot. The aircraft struck a boundary hedge within the solar farm complex. Both the pilot and the passenger sustained injuries, but they were able to exit the aircraft before it was destroyed by fire.
The investigation
The AAIB examined the wreckage to determine the origin of the fire. The investigation found that the engine compartment and much of the fuselage had suffered severe fire damage, including a partially melted crankcase. While the fuel hoses and connections to the fuel pumps and carburettor were recovered, the intensity of the fire and the impact prevented a definitive assessment of their condition.
Investigators noted that the right wing's fuel tank ruptured upon impact, while the left tank remained intact with 28 litres of fuel remaining. The investigation also noted that the aircraft's low airspeed at the moment of impact likely reduced the deceleration forces, which may have mitigated the severity of the injuries to the occupants.
Findings
- The engine instruments showed normal readings prior to the fire, suggesting the fire was likely caused by a fuel leak rather than an oil leak.
- The engine continued to operate for a short period after smoke appeared, which is consistent with fuel being supplied from the carburettor float bowl despite a leak elsewhere in the system.
- The heat from the engine's exhaust system was sufficient to cause the leaking fuel to auto-ignite.
- The specific source of the fuel leak could not be identified due to the extensive damage caused by the fire and the impact.