The Australian Transport Safety Bureau believes the pilot of Cessna C208B VH-FAY was a victim of hypoxia, when his aircraft flew uncontrolled into the ocean off the east coast of Japan in September 2018
The Caravan was on a ferry flight from Perth to the United States when it departed from Saipan Airport for New Chitose Airport in Japan. Nearly four hours into the leg, the pilot missed a position report, after which Tokyo Radio made repeated attempts to contact the pilot, without success.
Two Japan Air Self-Defense Force (JASDF) aircraft intercepted the Cessna, but the pilot did not respond to the intercept. The JASDF pilots were unable to see into the cockpit to determine whether the pilot was in his seat or whether there was any indication that he was incapacitated.
After about 30 minutes, the JASDF pilots watched the aircraft descend into cloud. The Caravan disappeared from radar less than 2 minutes later. Within 2 hours, search and rescue personnel located the aircraft’s rear passenger door. No other aircraft parts were located and the pilot was not found.
The ATSB concluded that the pilot became incapacitated whilst the aircraft was cruising on autopilot and the engine stopped after the pilot failed to change tanks, causing VH-FAY to descend into the ocean.
Director Transport Safety Stuart Macleod said that while the cause of the incapacitation could not be determined, the pilot was operating alone in an unpressurised aircraft at 22,000 feet and probably using an unsuitable oxygen system, which increased the risk of experiencing hypoxia.
“Operating unpressurised aircraft above 10,000 feet requires careful oxygen management and planning,” Macleod said.
“Where an increased risk of hypoxia exists, good risk management practices should be used for flight planning. Because the effects of hypoxia can be insidious, training in recognition of early symptoms of hypoxia can increase the time available to react, descend and resolve any issues.”
According to the ATSB investigation report, the oxygen system the pilot used may not have provided an adequate supply.
"There was adequate oxygen on board for the flight, however the pilot was probably using a nasal cannula connected to the pilot's electronic pulse demand system (EDS) at all flight levels as indicated by the fact that the Cessna [oxygen] mask was unused by the time the aircraft was in Saipan, despite having flown above FL180. This increased the risk of oxygen-blood saturation levels.
"The pilot had also indicated his intention to connect the EDS to the aircraft system without the in-line regulator that was required to ensure the EDS operated within its limits."
The ATSB also said the risk of hypoxia would have been mitigated if the pilot had used the available Cessna oxygen mask.
The full investigation report is on the ATSB website.