What happened
On January 7, 2006, a Robin DR 400-140 operated by a flying club was conducting a local instructional flight near Saint-Cyr-l'Ecole. The flight was intended to be a one-hour session to assist a pilot in extending their private pilot license.
Prior to departure, the pilot noted that the aircraft's single tank appeared to contain only about 25 liters of fuel. To ensure sufficient reserves, the crew attempted to refuel the 110-liter tank. During the process, the refueling nozzle automatically clicked off, and fuel began spilling from the filler neck. After a second attempt yielded the same result, the crew concluded that the tank was already full and assumed the fuel gauge was malfunctioning, as it indicated approximately one-quarter capacity.
After taking off, the aircraft flew toward Toussus-le-Noble and then maneuvered west of Saint-Cyr-l'Ecole. Approximately 50 minutes into the flight, the low fuel warning light illuminated. The instructor requested priority landing from air traffic control, and the aircraft returned to Saint-Cyr-l'Ecole, landing on runway 12. Upon landing, the crew discovered that 90 liters of fuel were required to complete the refueling process.
The investigation
The investigation focused on the refueling process and the crew's interpretation of the fuel levels. It was determined that the refueling nozzle had been held at an unusual angle because the pump hose had not been sufficiently unrolled. This positioning prevented the fuel from flowing normally into the tank, causing the nozzle to trigger prematurely and leading to fuel spillage.
Findings
- The primary cause of the incident was an incorrect refueling procedure caused by the improper positioning of the refueling nozzle.
- A decision-making error occurred when the crew interpreted the fuel overflow and the gauge reading as evidence of a full tank rather than a blockage or improper filling.
- The fuel level was significantly lower than the crew had estimated during pre-flight preparations.