Incident Overview
A single-pilot airplane on the final leg of a multi-day cross-country trip experienced a loss of communication and eventually crashed. The aircraft was not pressurized but was equipped with an oxygen system.
Flight and Communications
Radio contact with air traffic control (ATC) was normal until the airplane deviated 400 feet above its assigned altitude of FL240. When notified, the pilot stated he was trying to view his contrails. Later, after leveling at FL270, the pilot asked ATC if they had heard his earlier transmissions. That was the last message received; subsequent attempts to contact the pilot failed.
Interception and Descent
When the pilot did not begin descent or join the arrival route for the destination, ATC requested assistance from the North American Aerospace Defense Command (NORAD). Fighter aircraft intercepted the airplane but could not see the pilot inside the cockpit. Efforts to attract the pilot's attention were unsuccessful. The airplane eventually descended and struck terrain.
Oxygen System Findings
A nasal cannula was found attached to the aircraft's installed oxygen system, lying near the pilot. The pilot was wearing an oxygen mask connected to a portable oxygen bottle on the floor. Both systems were functional and their valves were open, but both were depleted of oxygen. The portable bottle was originally manufactured for industrial use and had been fitted with an oxygen system connector; its regulator was a medical-industry product.
Pilot's Practices and Equipment
A pilot's journal indicated he regularly flew at high altitudes for efficiency and monitored his blood oxygen with an oximeter. He typically used a nasal cannula above 18,000 feet and had used a combination of cannula and mask up to 31,000 feet. Examination of his hangar revealed an aircraft oxygen tank and a welding tank connected to an oxygen-service fitting. Neither the aircraft's oxygen system nor the portable bottle had been serviced at airports visited during the trip.
Advisory Circular (AC) 61-107A recommends that preflight inspections include a thorough check of oxygen equipment and supply, and that systems be checked frequently at altitude. It advises initiating an emergency descent below 10,000 feet if supplemental oxygen is unavailable, and cautions that continuous-flow oxygen systems above 25,000 feet require very careful attention to system capabilities.