What happened
On June 11, 2006, a Canadair CL-415, registration I-DPCP, was conducting a post-inspection test flight near Sutri, Italy. The flight was intended to certify the aircraft for service following a heavy maintenance 3C inspection. The crew, consisting of two pilots and a line technician, departed from Rome Ciampino.
During the flight, the crew noticed a significant discrepancy in fuel levels between the left and right wing tanks. While they initially attempted to balance the fuel using the transfer valve, they later discovered an excessive rate of fuel consumption. A visual inspection by the technician confirmed a visible fuel trail streaming from the left wing. To prevent a total fuel exhaustion, the crew executed a precautionary water landing on Lake Bracciano. There were no injuries and no fatalities during the incident.
The investigation
The ANSV investigation focused on the source of the leak and the maintenance history of the aircraft. Investigators found that the fuel filler cap for the left tank had displaced from its seat, and the sealing gasket was damaged in two places. The aircraft had recently undergone extensive maintenance, including work on the left wing tank. While the inspection records showed a visual check of the wing surface, they did not include a specific check of the fuel filler neck.
Investigators examined the fuel cap (P/N 457-370C) and found no mechanical defects or closure mechanism failures that would allow it to pop out if properly secured. Consequently, the investigation concluded that the cap was likely not correctly closed or locked following the recent maintenance work.
Findings
- The primary cause of the fuel loss was the displacement of the fuel filler cap from its seat, likely due to incomplete or incorrect installation following maintenance.
- Aerodynamic suction (low pressure) created on the upper wing surface during flight drew fuel out of the tank.
- The crew's monitoring of fuel consumption was inadequate, as their attention was primarily focused on the complexities of the test flight procedures.
- The crew's initial oversight regarding the fuel imbalance was compounded by the fact that the aircraft was carrying more fuel than required for the planned mission.