Pilot of Crashed 'Unresponsive Aircraft' Possibly Suffered Loss of Oxygen

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The cause of the crash of a small plane that stopped responding to radio calls, prompting a chase by fighter jets, was not immediately clear Friday — but experts believe that hypoxia, or loss of oxygen, possibly incapacitated the pilot and passenger.

Military pilots who chased the aircraft reported that a person was slumped over in the pilot seat, leading them to believe the cabin had lost air pressure. Depressurization can occur when aircraft rise too high or if there is an air leak, leaving little oxygen for passengers to breathe.

"We need to descend," the pilot told controllers when the craft was at 28,000 feet, according to audio collected by LiveATC.net. "We have an indication that is not correct on the plane." The controller gave permission to fly at 25,000 feet, and then to 20,000 feet -- but at that point the pilot didn't respond to calls, U.S. officials told NBC News.

"When you hear about cases like this, [hypoxia] is the most immediate thing that comes to mind," Dr. Dean Olson, program director of Wright State University's Aerospace Medicine Residency Program, told NBC News.

The plane was registered to real estate developer Larry Glazer, and he and his wife Jane were the only people on board, their son Ken told CNBC. It was reported to have been heading from Rochester, N.Y., to Naples, Fla.

Serious effects of hypoxia typically start at altitudes of around 8,000 to 10,000 feet, Olson said, and the passengers may not have known that they were suffering from a loss of oxygen. The effects of hypoxia on individual bodies can vary — so much so that pilots and aerospace physicians train in hypoxic chambers to ensure they can recognize their individual symptoms, he said.

Victims do generally experience a few particular symptoms: change in vision, like the loss of ability to sense color; increased breathing and heart rates; heavy or even euphoric feelings; and loss of consciousness. Others may notice a bluish color to their fingers, toes or nose, or suffer from a headache and lack of coordination. After an extended period without oxygen, brain activity slows and organs can shut down.

Earlier this summer, officials suggested hypoxia could have been to blame in the disappearance of Malaysia Airlines Flight MH370. In 1999, golf phenom Payne Stewart died in a Learjet crash in which officials cited cabin depressurization and ultimately hypoxia as the cause of death of all on board.