What happened
On August 12, 2001, a pilot was conducting an aerobatic training session in an amateur-built Bi-Louis aircraft, registration F-PENA, at the Marmande aerodrome. Following refueling, the pilot departed the airfield to begin the training flight. While performing a safety maneuver known as a 'mise dos' at approximately 2,500 feet, fuel entered the cockpit, splashing the pilot's face and torso.
Recognizing the danger, the pilot declared an emergency and requested priority landing. Due to the fear of fire, the pilot shut down the aircraft's electrical power. To mitigate the effects of the fuel vapors, the pilot initially cracked the canopy open for ventilation. When this proved insufficient, the pilot opened the canopy fully, which resulted in the canopy shattering instantly. The pilot subsequently completed an emergency landing without further injury.
The investigation
The investigation focused on how fuel was able to enter the cockpit and why the pilot was unable to detect the issue during pre-flight checks. Investigators located the fuel cap near the refueling pumps, confirming it had been left off after the previous refueling session.
Regarding the aircraft's configuration, the investigation noted that the forward fuel tank filler neck is positioned directly in front of the windshield, aligned with the compass. Because the pilot sits in the rear seat during aerobatic flight, the compass obscures the view of the filler neck, making it impossible for the pilot to visually verify if the cap is in place from the rear seat position.
Findings
- The primary cause of the incident was the failure to replace the fuel cap after refueling.
- The pilot was unable to verify the cap's presence because the cockpit's compass obscured the view of the filler neck from the rear seat.
- Inadequate sealing between the windshield and the canopy likely facilitated the fuel'ert entering the cabin during flight maneuvers.