What happened
On Friday, June 11, 1999, at approximately 14:00, a Yakovlev Yak-52 (registration RA-22527) was conducting a local flight near Voinsles, France. The aircraft was flying in formation with another aircraft of the same type, performing maneuvers along an aerobatic axis. After roughly 35 minutes of flight time—which included approximately 10 minutes of aerobatic maneuvers—the pilot notified the passenger of an engine problem. Although the pilot attempted to follow engine failure procedures, the engine ceased operation. The pilot performed an emergency landing in a field with the landing gear retracted. Upon impact, the aircraft overturned onto its back and came to a rest. The accident resulted in two injuries and significant damage to the aircraft.
The investigation
The investigation focused on the cause of the engine failure and the state of the aircraft's fuel supply. Post-accident inspections revealed that the fuel tanks were empty. Investigators found no evidence of fuel leaks, spills, or the smell of fuel in the vicinity of the aircraft. A subsequent disassembly of the fuel filter confirmed that the engine had suffered from fuel exhaustion.
Analysis of the fuel consumption rates showed that the engine consumes 60 L/h during cruise and 80 L/h during aerobatic flight. While the flight logs indicated a certain amount of fuel, the investigation revealed that 15 minutes of taxiing and engine testing had occurred after the last refueling, which was not recorded in the aircraft's logbook. Based on the flight duration and maneuvers, the estimated fuel remaining at the start of the flight was approximately 39 liters.
Findings
- The primary cause of the engine failure was an incorrect evaluation of the fuel quantity on board.
- During the pre-flight inspection, the pilot noted a discrepancy between the fuel gauge readings and a visual check performed by himself and the pilot of the accompanying aircraft. Based on this, the crew concluded that the remaining fuel was sufficient for the intended flight.
- The pilot's calculation of remaining endurance was based on an estimated average consumption of 42.5 L/h, which did not account for the higher consumption required during aerobatic maneuvers.
- The pilot was unaware of the 15 minutes of ground operations (taxiing and engine tests) that had depleted the fuel reserves, as these were not documented in the aircraft's logbook.