What happened
On 18 April 2001, a Reims Cessna FA152, registration G-BILK, was conducting a cross-country training exercise from Exeter Airport to Compton Abbas. The flight was operated by an instructor and a student under favorable weather conditions. Before departing Exeter, the instructor noted an imbalance in the long-range fuel tanks, with the left tank at half full and the right at one-quarter. This was attributed to the aircraft being parked on an uneven surface overnight.
After completing the outbound leg to Compton Abbas without incident, the crew prepared for the return flight. During the return journey, approximately 4 nautical miles from Exeter, the aircraft suffered a total power loss. The instructor assumed control, declared a 'Mayday', and performed emergency engine failure procedures. While manipulating the throttle provided intermittent power, it was not enough to maintain flight. The aircraft performed a forced landing in a small field, where the nose gear became embedded in soft ground, causing the aircraft to pitch inverted. Both occupants escaped the no injuries.
The investigation
The investigation focused on the fuel levels and the accuracy of fuel measurement methods used by the flying club. Post-accident examination of the engine revealed the carburettor heat was set to hot, the mixture was fully rich, and the fuel cock was open. While fuel analysis confirmed the use of correct AVGAS 100LL, investigators scrutinized the club's 'Flying Order Book' and the use of aircraft dipsticks.
It was discovered that the dipstick markings provided in the club's documentation were misleading. The documentation suggested much higher fuel volumes than were actually present. Specifically, a reading of 1/2 on the dipstick was interpreted as a much larger volume than the actual 7.6 gallons present in the left tank. This discrepancy meant the crew significantly overestimated the remaining endurance of the aircraft.
Findings
- The primary cause of the engine failure was an insufficient fuel supply to sustain the engine during the return leg.
- The pilot relied on an estimated fuel remaining based on the initial departure readings rather than re-dipping the tanks at Compton Abbas.
- The club's documentation regarding dipstick markings was inaccurate, leading to a significant overestimation of the total usable fuel on board.
- It is suspected that the engine was primarily being fed by the right tank during the outbound leg, leaving the right tank nearly empty upon departure for the return leg.