What happened
On 3 May 2025, a Spitfire Mk IXT, registration G-BMSB, was conducting a passenger flight in formation with another aircraft near Hythe, Kent. Approximately 35 minutes into the flight, the pilot detected a slight vibration in the engine, which was immediately followed by a rapid loss of power. The pilot observed dark smoke from the exhausts and noted a strong smell of fuel within the cockpit.
In an effort to maintain control, the pilot attempted to adjust the throttle, but the engine failed to recover power. After establishing a stable glide, the pilot identified a suitable field for a forced landing. To preserve airspeed and energy, the pilot elected to keep the landing gear retracted. The aircraft landed on its underside in the field, where it came to a stop. While the pilot was uninjured, the passenger suffered minor injuries.
The investigation
Following the incident, the AAIB examined the aircraft's engine and fuel system. The investigation established that a gasket within the pressure switch for the fuel low-pressure warning light had failed. This switch, which is attached to the carburettor, had developed an external leak because the securing screws had loosened.
This failure allowed pressurized fuel to spray into the lower rear section of the engine bay and into the air filter box. The fuel was subsequently drawn into the airflow, causing the engine to run an extremely rich mixture, which triggered the vibration and the subsequent loss of power.
Findings
- The engine power loss was caused by a degraded gasket within the fuel low-pressure warning switch assembly.
- The failure was likely due to the age of the component, as the switch was at least 70 years old.
- The leakage of fuel into the induction system created an excessively rich fuel-air mixture.
- The pilot's decision to maintain a high glide speed by not lowering the landing gear contributed to the successful outcome of the landing.