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Timeline perplexes U.S. aviation experts

WASHINGTON - U.S. aviation experts say they can't understand the behavior of the flight crew aboard a Cypriot airliner that crashed north of Athens after flying on autopilot for what could have been hours.

Early reports indicated the Helios Airways jet lost cabin pressure. Temperatures and oxygen levels would have plummeted and left everyone aboard unconscious and freezing to death as the plane flew on autopilot long before it crashed, experts said Monday.

But if there was a sudden decompression, experts say, the pilots and the flight attendants for some reason didn't react the way they were trained to.

"It's odd," said Terry McVenes, executive air safety chairman for the Air Line Pilots Association, International. "It's a very rare event to even have a pressurization problem, and in general crews are very well trained to deal with it."

The aircraft flew into Greek airspace, but air traffic controllers couldn't raise the pilots on the radio, and fighter jets intercepted the plane, flying at 34,000 feet.

The fighter pilots saw that the pilot wasn't in the cockpit, the co-pilot was slumped over his seat and oxygen masks dangled, government spokesman Theodoros Roussopoulos said. He said the air force pilots also saw two people possibly trying to take control of the plane.

It is that sequence of events that puzzles aviation experts.

Warnings should go off if an airliner suddenly loses pressure, and pilots are trained to immediately put their oxygen masks on and dive to about 12,000 feet, where there's enough oxygen for people to breathe, they say.

If a cabin loses pressure suddenly, passengers and flight crew have only seconds to put on oxygen masks before losing consciousness. Death would follow quickly.

The fire department has said none of the bodies had masks on their faces. And the chief Athens coroner said at least six of the victims were alive at the time of the crash.

The pilots also didn't report any windows out or holes in the fuselage, the most likely causes of a catastrophic loss of pressure, said Bill Waldock, an aviation safety professor at Embry-Riddle Aeronautical University in Arizona.

Another clue to a sudden pressure loss would have been frost on the windows because it's so cold at 34,000 feet, said Waldock. But if the fighter pilots could see into the cockpit, the windows couldn't have been iced over.

Paul Czysz, emeritus professor of aerospace engineering at St. Louis University, wonders why the co-pilot was slumped over.

"He couldn't have been unconscious for a small decompression at 34,000 feet," Czysz said. "Something's amiss."

The pilot and the co-pilot would have had five times as much oxygen as the passengers, he said.

"Even if the pressurization system was failing, it doesn't fail instantaneously. Even if it goes fast, you can seal the cabin, you've got all the oxygen in the cabin to breathe, you've got the masks and you've got plenty of time to get to 12,000 feet," Czysz said.

Jim Hall, former chairman of the National Transportation Safety Board, said it's possible the oxygen in the cockpit failed. He said the NTSB has been concerned about the ability of pilots to get their masks on quickly enough. "The accident did not have to occur," Hall said. "It has to be either a training issue or an equipment issue."

[Last modified August 16, 2005, 01:30:10]