Mystery at 35,000 Feet

Aug. 15, 2005 — -- Two black boxes from the Cypriot airliner with 121 people aboard that crashed Sunday near Athens have been recovered as Greece investigates the worst air disaster in its history.

Helios Flight ZU522 plowed into a hill after, authorities believe, an apparent drop in cabin pressure knocked out both pilots and passengers on the Boeing 737. Tests on the bodies appear to confirm that most of the victims were "frozen solid," and may already have been dead when the plane crashed.

Lack of oxygen was a contributing factor to the accident, but not the cause of the accident, ABC News aviation analyst John Nance said today.

"This one is very puzzling because the pieces don't seem to fit," Nance told ABC's "Good Morning America." He added that pilots learn early on in their training that at the first sign of a cabin pressurization problem, they should deploy oxygen masks and begin an emergency descent to a safer altitude.

Liz Verdier, a spokeswoman for Boeing, told The Associated Press that all Boeing planes are equipped with warning systems that alert pilots to a cabin decompression.

Nance said that the oxygen that comes through the masks is controlled from the cockpit and that if it had been turned off, the captain would have had fewer than 20 seconds of consciousness to turn the oxygen on, and to begin to take the plane to a lower altitude.

Cabin pressure problems are rare. In 1999, pro golfer Payne Stewart and four others were killed when their jet lost pressure and flew hundreds of miles on autopilot before crashing in South Dakota.

The pilots of Flight 522 reported air conditioning system problems to air traffic controllers shortly after takeoff. Within minutes, after entering Greek airspace over theAegean, the Boeing 737 lost all radio contact. Two Greek F-16 fighter jets were scrambled to investigate. The jets intercepted the plane at 34,000 feet, and pilots reportedly saw the co-pilot slumped over in his seat. The captain was not in the cockpit, and oxygen masks dangled inside the cabin, government spokesman Theodoros Roussopoulos said.