What happened
On 3 March 2024, a Beagle B121 Series 2 Pup, registration G-AZCZ, was engaged in a private flight from St Athan to Duxford. Due to deteriorating weather at the intended destination of Sywell, the pilot diverted to Duxford. After several hours on the ground, the pilot commenced the return flight to St Athan.
During the approach to St Athan, the pilot performed standard checks, which included switching the fuel source from the right tank to the left tank. Shortly after this change, the engine suffered a significant loss of power. The pilot observed that the fuel pressure had dropped to zero. Despite attempts to rectify the issue by switching between tanks, the engine failed to regain power. The pilot declared a MAYDAY and, unable to reach the runway, opted to land in a nearby field. During the landing roll, the aircraft's nosewheel struck soft ground, causing the plane to tip over. The pilot was uninjured, but the passenger sustained one minor injury to her shoulder. The aircraft was damaged beyond economic repair.
The investigation
The AAIB examined the aircraft's fuel systems and the pilot's flight planning. Investigators found that the aircraft's fuel tanks were empty upon inspection. The investigation also looked into the discrepancies between the aircraft's Approved Flight Manual (AFM) and the airworthiness specifications regarding unusable fuel. While the AFM was ambiguous, historical data indicated that approximately 1 imperial gallon of fuel was unusable due to its position in the tanks.
Furthermore, the investigation reviewed the pilot's fuel calculations for the return leg. The pilot had estimated the remaining fuel based on a visual check of the tanks rather than cockpit gauges, which he did not fully trust. The investigation also noted that the pilot's planning did not account for the fuel consumed during taxiing, engine start, or the initial climb phase.
Findings
- The engine power loss was most likely caused by fuel starvation.
- The pilot's fuel planning failed to account for the volume of unusable fuel in the tanks.
- The flight plan did not include allowances for fuel consumption during ground operations or the takeoff climb.
- There was a lack of clarity in the aircraft's documentation regarding whether the total fuel capacity included or excluded unusable fuel.
- The pilot's reliance on visual fuel estimation during pre-flight checks contributed to the error in calculating remaining endurance.