What happened
On 13 July 2005, a Whitaker MW6 Merlin, registration G-MYZA, was engaged in a private flight near Newent, Gloucestershire. The pilot had previously flown to a club meeting and was returning to his home airstrip. While flying at approximately 200 ft altitude, the engine suddenly stopped.
To avoid fields containing crops, the pilot attempted a 90-degree right turn to reach a grass area adjacent to the airstrip. During this maneuver, the aircraft passed near a group of trees. The pilot reported that the trees shielded the aircraft from the wind, causing a loss of airspeed. The aircraft subsequently stalled and impacted the ground in a nose-down attitude. The impact caused extensive damage to the aircraft, but the pilot escaped with only minor injuries.
The investigation
The AAIB examined the engine failure and the circumstances surrounding the fuel system. The aircraft was operating on MOGAS1, which had been refilled that morning from a different batch than the fuel already in the tank. The investigation considered two primary possibilities for the engine stoppage: the presence of contaminants, such as water, or the occurrence of vapour lock.
While the pilot noted reports of a paraffin-like smell in the exhaust and had sent fuel samples for analysis, the results remained inconclusive. The investigation also noted that the pilot did not perform a fuel water test prior to takeoff. Furthermore, the aircraft had been parked overnight with a partially full tank, which can lead to condensation.
Findings
- The engine failure was most likely caused by vapour lock within the fuel supply.
- This phenomenon was likely triggered by high ambient temperatures (between 24°C and 27°C) combined with heat from the engine and potential sunlight heating the wing tank.
- The aircraft stalled at a low altitude during a turning maneuver, leading to the ground impact.