NYC06FA079 · Beech 56TC

While on the last leg of a multiple day cross-country trip, all communications between the pilot of a non-pressurized, oxygen system equipped airplane, and air traffic control (ATC) were normal until the airplane was detected to have climbed 400 feet above its assigned altitude of FL240. After being notified of the deviation, the pilot responded that he was attempting to look at his contrails. Later in the flight, after leveling at FL270, the pilot queried ATC as to whether they had heard some of his previous calls. This was the last transmission received from the pilot, and attempts to reestablish contact were unsuccessful. After the pilot had not begun his descent for landing, nor joined the arrival course for his destination, ATC requested assistance from the North American Aerospace Defense Command (NORAD). After intercepting the airplane, the pilots of the fighter airplanes attempted to look into the cockpit, but were unable to see the pilot. Attempts to gain his attention were also unsuccessful. The airplane eventually descended and impacted terrain. A nasal cannula was connected to the airplane's installed oxygen system and was found near the pilot. An oxygen mask the pilot was wearing was connected to a portable oxygen bottle found on the floor next to him. Both systems were functional, their valves were open, and both were depleted of their contents. The portable bottle was manufactured for industrial use, and modified with an oxygen system fitting. The regulator was manufactured for the medical industry. A review of a journal kept by the pilot revealed that he flew at high altitudes for efficiency, and used an oximeter to monitor blood oxygen. He used a nasal cannula at altitudes exceeding 18,000 feet for comfort, and had used a "cannula and mask" up to 31,000 feet. Examination of his hangar revealed an aircraft oxygen tank and welding tank plumbed to an oxygen-service fitting. The airplane's oxygen system or portable bottle had not been serviced at the airports the airplane operated from during the trip. According to Advisory Circular (AC) 61-107A, "Operations of Aircraft At Altitudes Above 25,000 Feet MSL And/Or Mach Numbers (MMO) Greater Than .75", preflight inspections should include a thorough examination of aircraft oxygen equipment, "including available supply," and that "Oxygen systems should be checked periodically to ensure that there is an adequate supply of oxygen and that the system is functioning properly. This check should be performed frequently with increasing altitude. If supplemental oxygen is not available, an emergency descent to an altitude below 10,000 feet should be initiated." Additionally, it advised that when using continuous flow oxygen systems above 25,000 feet, "very careful attention to system capabilities is required."

Verbatim NTSB analysis and probable cause from the NTSB dataset