Accident Sequence
Air traffic control (ATC) cleared the pilot of an unpressurized airplane to climb to 25,000 feet. Radar data showed the aircraft passing through the assigned altitude and leveling at 27,700 feet, then descending to 26,000 feet, after which contact was lost. ATC queried the pilot about the altitude deviation, but no response was received. The aircraft subsequently experienced an inflight breakup during an uncontrolled descent and came to rest in a tree.
Passenger Account
A surviving passenger reported that the airplane had been refueled and a portable oxygen bottle filled before takeoff. The flight was intended for aerial photography at four separate locations. After completing three locations, the aircraft landed at Williamsburg, Pennsylvania, where the pilot filed a flight plan and set up the portable oxygen system for continued use. On departure, the aircraft climbed to 10,000 feet, at which point the pilot instructed the passenger to put on her oxygen mask, and he did the same. The passenger recalled the last altitude she heard the pilot call out was 20,000 feet; he asked how she was feeling, and she replied that she felt fine. When asked who turned on the oxygen, she stated that she attempted to do so but was unsure of the procedure, so the pilot reached back and activated it. She confirmed the system was on because she felt cool air and observed a small valve in each line change from red to green, indicating oxygen flow. Shortly after crossing 20,000 feet, she began feeling dizzy, her eyes would not focus, and she felt cross-eyed. She informed the pilot, but believed he was occupied communicating with the tower and did not respond. She found relief by closing her eyes, after which she had no clear memory until after the crash.
Oxygen System Analysis
Analytical testing was conducted on the contents of the cylinders used to fill the pilot's portable oxygen bottle. The test results indicated that the cylinders contained compressed breathing air with approximately 21 percent oxygen, rather than the required aviation oxygen.
Pilot Postmortem
Postmortem examination determined that the pilot's death resulted from hypoxic hypoxia due to insufficient oxygen reaching the blood.