What happened
On 7 June 2022, a Cessna U 206, registered F-BXAM, was conducting a parachute drop training flight near Punaauia, French Polynesia. The flight was operated by SARL Tahiti parachutisme and carried an instructor pilot and a pilot in instruction.
After completing the parachute drop at FL 97, the instructor pilot initiated a series of descending turns with a 45-degree bank angle to train the student pilot. While descending through approximately 4,500 feet, the crew experienced a sudden and significant reduction in engine power. Despite various attempts by the crew to restart the engine using the power lever, mixture control, and starter, the engine failed to recover.
The instructor pilot declared a MAYDAY and identified the lagoon near the Méridien hotel as the intended landing site. The aircraft ditched in the lagoon, turning over upon impact with the water. Both occupants were able to evacuate the aircraft and sustained no injuries.
The investigation
Investigators examined the wreckage and the propulsion system, including the Continental IO-520-F engine. While corrosion from seawater immersion prevented many functional tests, several key findings were established:
- The engine's crankshaft rotated freely, and no internal structural failures were found.
- Analysis of the Engine Display Monitoring (EDM) data showed a brief increase in Exhaust Gas Temperature (EGT) followed by a sudden drop, a pattern characteristic of a transient lean mixture caused by fuel starvation.
- Testing of the fuel pump assembly revealed that the fuel flow rates did not match the manufacturer's specifications; the pump's setting screw required adjustment to meet required standards.
- The maintenance provider had not adjusted the fuel system settings during recent inspections, noting a lack of specialized calibrated tools required by the manufacturer.
Findings
- The engine shutdown was likely caused by fuel starvation of the fuel system during the descent maneuvers.
- At the time of the failure, the right fuel tank contained 30 liters, which was less than one-quarter of its capacity. The aircraft's manual specifies that flying in uncoordinated configurations, such as sideslips or banked turns, when fuel levels are low can lead to starvation.
- The crew struggled to identify the nature of the engine failure during the emergency, and the instructor did not implement the specific procedures for fuel starvation, such as activating the auxiliary fuel pump.