Uncontrolled flight into water accident investigation highlights the risks of hypoxia

The pilot of a Cessna Grand Caravan was almost certainly incapacitated, possibly from hypoxia, when his aircraft flew uncontrolled into the ocean off the east coast of Japan.   

The Australian-registered Cessna 208B (VH-FAY) was being ferried from Perth to Mississippi in the United States via the Northern Pacific when on the morning of 27 September 2018 it departed from Saipan Airport in the Northern Mariana Islands bound for New Chitose Airport in Hokkaido, Japan.

After climbing for about an hour, the aircraft levelled off at 22,000 feet, while after 2 hours and 20 minutes into the flight, the pilot contacted Tokyo Radio flight information service on HF radio to make a mandatory position report. The aircraft was next due to report about an hour and 20 minutes later, when overhead the SAGOP reporting point, but no contact with Tokyo Radio was made. Tokyo Radio subsequently made repeated attempts to communicate with the pilot, without success.

About 4.5 hours after the pilot’s last communication, two Japan Air Self-Defense Force (JASDF) aircraft intercepted the Cessna. The pilot did not respond to the intercept in accordance with international intercept protocols, either by rocking the aircraft wings or turning, and the aircraft continued to track at 22,000 feet on its planned flight route. 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 observed the aircraft descend into cloud. The aircraft descended rapidly and 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.

Rear passenger door

Rear passenger door. Source: Aircraft operator

Source: Aircraft operator

The ATSB’s subsequent investigation found that while the aircraft was in the cruise on autopilot, the pilot almost certainly became incapacitated. Consequently, about 5 hours after the last position report, without pilot intervention to change fuel tanks, the aircraft’s engine stopped, likely due to fuel starvation. This resulted in the aircraft entering an uncontrolled descent into the ocean.

The effects of hypoxia can be insidious.

Director Transport Safety Stuart Macleod said that while the cause of the incapacitation could not be determined, and a medical event could not be ruled out, 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,” Mr 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.”

As a result of this accident, the aircraft operator amended its operation manual to include additional guidance for international ferry flights. It also created an oxygen-use guide and a specific risk assessment for positioning (ferry) flights.

Read the report AO-2018-065: Collision with water involving Cessna 208B, VH-FAY, 260 km north-east of Narita International Airport, Japan, on 27 September 2018

Last update 18 March 2020