Canadian authorities appear to have a well-documented and recorded case of hypoxia in their investigation of the stall/spin fatal accident involving a Piper Navajo a year ago. On Aug. 1, 2018, an Aries Aviation PA-31, a well-maintained aircraft regularly flown by experienced pilots, inexplicably spun into a 10,000-foot mountain peak while on initial descent to Calgary/Springbank Airport. The aircraft and the pilot and technician on board carried out aerial survey work near Penticton in southern British Columbia and were on their way home at a flight-planned altitude of 15,000 feet when the pilot become confused and lost control of the aircraft about an hour into the flight. Thanks to an aftermarket data recorder on the aircraft, Transportation Safety Board investigators were able to reconstruct what appears to be a classic case of the insidious nature of hypoxia.
The commercially-operated Navajo did not require a cockpit voice recorder or flight data recorder but the owner installed an Appareo Systems Vision 1000 and a J.P. Instruments engine data monitor. The Appareo device recorded flight parameters, video, radio and intercom and the investigators watched as a normal hop over the Rocky Mountains that separate B.C. and Alberta for this crew turned into tragedy. After two hours of flying grids near Penticton, the pilot filed an IFR flight plan in the air back to Calgary at 15,000 feet, 2,000 feet above the legally mandated altitude for using supplemental oxygen. The aircraft was properly equipped and the camera recorded the pilot briefly holding an oxygen mask to his face early in the flight but he did not put it on. He set the autopilot and the flight proceeded normally. As the plane approached Calgary an hour later, controllers started sequencing it into the busy airspace, starting with a descent to 14,000 feet. In the next few minutes, the pilot misunderstood requests for flight information and engine settings were changed asymmetrically. Within minutes, the stall horn was on and the Navajo finally slumped right into a 7.5-rotation spin into the side of the mountain. The TSB determined the pilot was “likely hypoxic” and that led to the spin and his failure to recover from it.