What happened
On May 6, 2007, a SOCATA Rallye 235 E, registration F-BXYU, was engaged in glider towing operations departing from Sisteron aerodrome. During the initial climb phase, the pilot encountered a wind gust that required significant control inputs. During this period, the engine stopped. The pilot instructed the glider pilot to release the tow cable and prepared for an emergency landing.
While the engine briefly restarted, it failed again shortly thereafter. During the approach to a nearby field, the pilot switched the fuel selector to the right tank, which caused the engine to restart. However, due to the low altitude, the pilot determined that a go-around was not possible and proceeded with the emergency landing in the field. The glider pilot subsequently returned to the aerodrome to land.
The investigation
The investigation focused on the fuel levels and the pilot's pre-flight inspections. The pilot had checked the fuel quantities via the filler ports, noting that the right tank was full with approximately 80 liters. However, the pilot was unable to visually determine the exact level in the left tank.
To supplement this, the pilot checked the electrical fuel gauges on the instrument panel. While the right gauge indicated a full tank, the pilot misread the left gauge. The pilot incorrectly interpreted the gauge to mean that the left tank was missing 20 liters, leading to the erroneous belief that 60 liters remained in that tank, when in reality, only approximately 20 liters were present.
Findings
- The primary cause of the engine failure was fuel exhaustion resulting from an incorrect interpretation of the cockpit fuel gauges during the pre-flight inspection.
- A lateral wind gust or the pilot's reaction to said gust may have contributed to the interruption of the engine's fuel supply.
- The pilot's mental calculation of the remaining fuel in the left tank was inaccurate due to the misread gauge.