Background
On November 6, 2020, about 1520 Pacific standard time, a Pilatus PC-12, registration N400PW, was substantially damaged when it was ditched in the Pacific Ocean approximately 1,000 miles east of Hilo, Hawaii, following a total loss of engine power. The two pilots on board sustained no injuries. The aircraft was being operated as a Title 14 Code of Federal Regulations Part 91 ferry flight.
The Flight
The pilot in command (PIC) and another pilot were ferrying a new airplane from California to Australia. The first transoceanic leg was planned for 10 hours, from Santa Maria Airport (KSMX), Santa Maria, California, to Hilo Airport (PHTO), Hilo, Hawaii. A subsidiary of the airframe manufacturer had installed an auxiliary ferry fuel line and check valve in the left wing after aircraft delivery to the United States. About one month before the trip, the PIC hired a ferry company to install an internal temporary ferry fuel system. The pilots attempted the first transoceanic flight on November 2, but the ferry fuel system did not transfer properly, so they diverted.
The system was modified with the addition of two 30-psi fuel transfer pumps that could overcome the airplane’s ejector fuel pump pressure and the ferry system check valve. The final system consisted of two aluminum tanks, two transfer pumps, transfer and tank valves, and associated fuel lines and fittings. The ferry fuel supply line was connected to the newly installed ferry fuel line fitting at the left-wing bulkhead, which then fed directly to the main fuel line through a check valve and directly to the engine fuel system. The system was ground- and flight-checked before the trip.
According to Federal Aviation Administration (FAA) automatic dependent surveillance broadcast (ADS-B) data, the airplane departed KSMX about 1000. For the accident flight, the main fuel tanks were full with 402 gallons, the No. 1 ferry tank contained 100 gallons, and the No. 2 ferry tank contained 60 gallons. A fuel utilization procedure was followed.
The first halves of the ferry tanks were transferred without issue except for occasional illumination of the FUEL IMBALANCE caution light, which was expected. Then the ferry system was used to transfer the remaining fuel from the No. 2 ferry tank. The airframe manufacturer noted that the fuel utilization procedure did not give the flight crew reliable situational awareness of the airplane’s fuel state, as it relied on information the crew did not have (motive flow rate) and on fuel quantity indications that were not accessible while transferring fuel.
About 3.5 to 4 hours into the flight, the airplane climbed from FL 200 to FL 280. About 5 hours in, with the No. 2 ferry tank almost empty, the pilots prepared to stop transferring fuel. After the transfer pump was turned off, the FUEL LOW PRESSURE light illuminated. The engine then surged, shut down, and feathered. The engine lost power about 20 seconds after turning the transfer pump off. The main tanks and No. 1 ferry tank held about 450 gallons at that time.
The pilots performed air start procedures; the engine started but never reached idle rpm, and manipulation of the power control lever had no effect. The engine did not fully start. During a subsequent start attempt, a loud grinding noise and then a loud catastrophic bang were heard. The Engine and Propeller Electric Control System (EPECS) FAIL light illuminated at some point. Despite multiple air start attempts, the propeller never moved and the engine never restarted. About 8,000 ft, the pilots committed to ditching.
Ditching and Rescue
The pilots donned life vests, prepared survival gear, and made mayday calls. The PIC performed a full-flaps, gear-up landing into the wind at an angle to sea swells estimated at 5 to 10 ft high with crests 20 ft apart. The airplane landed upright. The pilots evacuated through the right over-wing exit and boarded a six-person covered life raft. A photograph showed the rudder bottom was substantially damaged. The airplane remained afloat after ditching.
The pilots used a satellite phone to communicate with Oakland Center. The United States Coast Guard coordinated a rescue with the M/V Ariel, but initial rescue attempts were unsuccessful. The next afternoon, the M/V Horizon Reliance successfully rescued the pilots. They had been in the raft for about 22 hours. The airplane was lost at sea.
Aircraft and Fuel System Information
The aircraft was issued a Standard Certificate of Airworthiness on April 15, 2020. This model PC-12 was certified without an air separator in the engine fuel feed line, which was included on previous models. The production fuel system design did not require a Fuel System Icing Inhibitor (FSII).
On June 9, 2020, the ferry fuel system provisions were designed and installed by the manufacturer as a major alteration per FAA Form 337. The form stated that the ferry tank provisions feed directly into the engine's fuel supply line and that installation should ensure no air is introduced. However, the FAA Form 337 submitted by the company that installed the ferry tanks on October 28, 2020, stated that the ferry fuel feed was directly to the left main tank.
During positioning and attempted ferry flights on November 1 and 2, 2020, the ferry system would not transfer fuel. After modification with two pumps (November 2-5), the system was tested on November 6 up to 17,500 ft and worked. No further tests were conducted. The aircraft was returned to service and departed KSMX about 1000.
The installed ferry system altered fuel flow characteristics. Unlike the production system, the ferry system moved fuel to the engine feed line through a check valve at higher pressure, closing the flap valve in the delivery ejector pumps. Excess fuel returned to the wing tanks via the motive flow circuit.
FAA Advisory Circular 23-10 provides guidance on auxiliary fuel systems. After installation, no tests were performed to address altitude performance effects, failure mode and effects analysis, or verification of continuous engine operation upon auxiliary tank depletion.