Story ID: 
Known Oxygen System Deficiency Preceded Fatal Crash
By: Amy Wilder
Caption: Air Force intercept confirmed no cockpit or cabin activity before crash
Word Count: 453
A Cessna Citation 560 that flew unresponsive for nearly two hours before crashing into mountainous terrain in Virginia on June 4, 2023, had known unresolved deficiencies in its oxygen system, according to the NTSB’s final report. Although it could not be verified from medical evidence, investigators concluded that the pilot and passengers were likely incapacitated by hypoxia following a loss of cabin pressurization; the report also noted a lack of supplemental oxygen onboard.
Two days before the flight, maintenance reports documented that “the pilot-side oxygen mask was not installed, and the supplementary oxygen was at its minimum serviceable level. No evidence was found to indicate that the oxygen system was serviced or that the pilot-side oxygen mask was reinstalled before the accident flight.”
Four weeks prior, maintenance personnel identified 26 discrepancies that the aircraft owner declined to repair, including “several related to the pressurization and environmental control system.” On the day of the accident, five maintenance items remained overdue, including inspection of the copilot oxygen mask.
The 69-year-old ATP-rated pilot and three passengers had departed Elizabethton Municipal Airport (K0A9), Tennessee, at about 1:13 p.m. local time, en route to Long Island MacArthur Airport (KISP) in New York. While climbing through 26,600 feet, the pilot read back an ATC clearance to FL340 at 1:25 p.m., but when ATC amended the altitude to FL330 for traffic avoidance three minutes later, the pilot had stopped responding.
The aircraft continued along its original flight path at FL340 to the destination, then overflew the destination airport before turning southwest on autopilot and continuing for nearly an hour. It then entered a spiraling descent and finally crashed near Montebello, Virginia.
Intercepting Air Force pilots reported seeing “a person seated in the left cockpit seat, who was slumped completely over into the right seat and who remained motionless throughout their observations,” and “no movement” in the cabin. No oxygen masks were deployed, and no smoke, structural breaches, or window frost were observed. 
According to the NTSB, the lack of oxygen during a loss of cabin pressurization likely rendered all occupants incapacitated. “Altitude-related hypoxia, although not verifiable from forensic medical evidence, likely explains the incapacitation of the airplane occupants,” the NTSB noted. The probable cause was “pilot incapacitation due to loss of cabin pressure for undetermined reasons,” with a contributing factor being “the pilot’s and owner/operator’s decision to operate the airplane without supplemental oxygen.”
FAA guidance warns that at altitudes between 30,000 and 35,000 feet, pilots may have just 30 to 120 seconds of useful consciousness. Gradual depressurization can be particularly dangerous, as “cognitive impairment from hypoxia makes it harder for affected individuals to recognize their own impairment.”