Pilot of unresponsive private jet that crashed and killed 4 was seen slumped over, source says

(CNN)-The pilot of the unresponsive private jet that triggered an interception by supersonic military fighter jets protecting Washington, DC, was observed slumped over in his seat, a source familiar with the response told CNN.

The lone pilot and three passengers were aboard the

Cessna Citation that crashed in a heavily wooded area near Waynesboro, Virginia, the Federal Aviation Administration said Monday. There were no survivors, authorities said.

Another source told CNN that crash investigators are most interested in hypoxia– a shortage of oxygen in the blood – as a reason why the pilot and passengers didn’t respond to attempts by air traffic controllers and even other civilian aircraft to contact the ill-fated plane.

No survivors found at Virginia plane crash site after US fighter jets attempted to intercept its unresponsive pilot, police say

Hypoxia is an insidious risk of flying at high altitude and could have been brought on by a decompression of the jet’s pressurized cabin, aviation experts say. The flight was cruising from East Tennessee to Long Island, New York, at 34,000 feet, an altitude where pilots have 30 to 60 seconds to don oxygen masks when pressure drops or risk falling unconscious.

When F-16s reached the Cessna 560 Citation V around 3:20 p.m., the jet pilots set off flares in an effort to get the pilot’s attention, a Sunday news release from the Continental US North American Aerospace Defense Command Region said.

“The pilot was unresponsive and the Cessna subsequently crashed near the George Washington National Forest, Virginia,” the release said. “NORAD attempted to establish contact with the pilot until the aircraft crashed.”

The FAA lost contact with the jet just 15 minutes after it took off, according to a statement from the agency and data from air travel tracking website FlightAware.

Approximately eight minutes after losing contact, the agency contacted the “Domestic Events Network” that consists of the military, national security, homeland security and other law enforcement agencies, according to the FAA statement.

The civilian aircraft flew from Elizabethton, Tennessee, past its destination – New York’s Long Island MacArthur Airport – and turned back before eventually crashing in Virginia on Sunday afternoon, according to NORAD and LiveATC.net.

In addition to the F-16s, air traffic controllers and other civilian pilots frantically tried to contact the unresponsive crew of the jet by radio as it flew toward Washington, DC, at 34,000 feet, audio from LiveATC.net revealed.