What happened
On November 6, 2020, a Pilatus PC-12, registration N400PW, was ditched in the Pacific Ocean roughly 1,000 miles east of Hilo, Hawaii, following a total loss of engine power. The aircraft was operating as a Part 91 ferry flight, traveling from California to Australia.
During the flight, the crew was utilizing a temporary internal ferry fuel system. Approximately five hours into the flight, the crew prepared to stop transferring fuel from the No. 2 ferry tank. After the transfer pump was turned off, the engine surged and completely shut down. The crew attempted multiple engine air starts at altitude; however, during a subsequent start sequence, the engine produced a loud grinding noise and a catastrophic bang.
As the aircraft descended, the crew performed the ditching checklist. The pilot performed a full-flaps, gear-up landing into the sea swells. The two pilots were not injured and evacuated into a life raft. After being adrift for approximately 22 hours, the crew was rescued by the crew of a container ship.
The investigation
The investigation focused on the modified ferry fuel system, which included two 30-psi transfer pumps designed to overcome the aircraft's 10-psi ejector pump pressure and a check valve. The system connected the ferry tanks directly to the engine fuel supply line.
Analysis revealed that the ferry system altered the aircraft's fuel flow characteristics. Because the ferry pumps operated at a higher pressure than the delivery ejector pumps, the ejector pumps' flap valves closed. This caused unused fuel in the motive flow line to flow out of the delivery ejector pump inlets.
Additionally, the aircraft was certified without an air separator in the engine fuel feed line, and the production design did not require a Fuel System Icing Inhibitor (FSII). No evaluations were conducted to determine if the ferry system's operation would impact fuel system temperatures, the need for FSII, or the impact of not having an air separator.