AP Photo XDM101

By ELENA BECATOROS

Associated Press Writer

GRAMMATIKO, Greece (AP) - A Cypriot plane crashed into a hill north of Athens on Sunday, killing all 121 people on board in what officials called Greece's worse airline disaster. At least one of the pilots reportedly was unconscious when the plane went down, possibly from lack of oxygen.

The Helios Airways flight ZU522 was headed from Larnaca, Cyprus, to Athens International Airport when it crashed at 12:20 p.m. near the town of Grammatiko, about 25 miles north of the Greek capital, leaving flaming debris and luggage strewn across a ravine and surrounding hills.

The Boeing 737, carrying 115 passengers and six crew, was to have flown onto Prague, Czech Republic, after stopping in Athens.

The cause of the crash was unclear, but it was apparently a technical problem - possibly decompression - and not terrorism. ``The first indications, in Cyprus and in Greece, are that it was not caused by a terrorist act,'' said Marios Karoyian, a spokesman for Cypriot President Tassos Papadopoulos.

The head of the Greek airline safety committee, Akrivos Tsolakis, described the crash as the ``worst accident we've ever had.'' He said the plane's black boxes had bee discovered at the scene, containing flight data and voice recordings valuable for determining the cause.

``There apparently was a lack of oxygen, which is usually the case when the cabin is depressurized,'' Tsolakis said.

A man whose cousin was a passenger on the plane told Greece's Alpha television he received a cell-phone text message minutes before the crash. ``He told me the pilots were unconscious. ... He said: ``Farewell, cousin, here we're frozen,'' Sotiris Voutas said.

The plane lost contact with Greek and Cypriot air traffic control 23 minutes after take off.

Two F-16 fighter jets were sent out shortly after the plane entered Greek air space over the Aegean Sea but did not respond to radio calls - a standard Greek practice. As they intercepted the airliner shortly before it crashed, the jet pilots saw one of the pilots slumped unconscious over the controls, Alpha TV reported. It was unclear where the other pilot was.

The fighter pilots said there was no movement in the cabin. Some Greek media reports said fighter pilots also could see oxygen masks dangling inside the cabin, but officials could not confirm that.

``It looks like the plane was on automatic pilot'' when it crashed, Helios spokesman Marios Konstantinidis said at Larnaca airport, in Cyprus.

Greek state television quoted Cyprus Transport Minister Haris Thrasou as saying the plane had decompression problems in the past. However, another Helios representative, Giorgos Dimitriou, said at Athens airport that the plane had ``no problems and was serviced just last week.''

David Kaminski Morrow, deputy news editor of the British-based Air Transport Intelligence magazine, said depressurization is extremely serious because its effects happen so quickly.

``If the aircraft is at 30,000 feet, you don't stay conscious for long, maybe 15 to 30 seconds. It is like standing on top of Mount Everest,'' he said. ``But if you are down at 10,000 feet, you can breath for a lot longer.''

Airplane cabins are usually pressurized at 8,000 feet.

Sudden loss of cabin pressure was blamed for a similar crash that took place in South Dakota on Oct. 25, 1999. A private Learjet 35 lost pressure, leaving pro golfer Payne Stewart and four others unconscious. The twin-engine jet went down in a pasture after flying halfway across the country on autopilot.

In the Greek crash, the only piece of the plane that remained intact was the tail section. Bits of human flesh, clothing, and luggage were scattered around the wreckage, which also started brush fires around the area.

More than 100 firefighters, aided by eight special planes and three helicopters dropping water, fought a huge brush fire caused by the crash. Parts of the remains of the plane were engulfed by the fire. The plane broke up into at least three pieces: the tail, a bit of the cockpit and a piece of the fuselage section that witnesses said contained a large group of bodies.

Some of the dead were children, although it was not known how many.

Fire trucks and ambulances crowded roads near the crash site and dark black smoke could be seen rising from various sites around the crash. A number of black-robed Greek Orthodox Christian were also on the scene.

Rescue workers and residents on the scene said they had found no survivors.

``There is wreckage everywhere. I am here, things here are very difficult, they are indescribable,'' Grammatiko Mayor George Papageorgiou said. ``I am looking at the back tail. The fuselage has been destroyed. It fell into a chasm and there are pieces. All the residents are here trying to help.''

Helios Airways was founded in 1999 as Cyprus' first private airline. It operates a fleet of Boeing 737 jets to cities including London; Athens; Sofia, Bulgaria; Dublin, Ireland; and Strasbourg, France.