The tail of a crashed Helios Airways plane is seen in this August 14 photo. (File Photo/AP)

The Helios Airways flight HCY 522 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 737-300, carrying 115 passengers and six crew, was to have flown onto Prague, Czech Republic, after stopping in Athens.

"The fire is still burning and there are no survivors," fire chief Christos Smetis said.

The cause of the crash was unclear, but early indications were that it was a technical problem — possibly decompression — and not terrorism. The plane's black boxes, which contain flight data and voice recordings, had been recovered at the scene, state NET television reported.

"The first indications, in Cyprus and in Greece, are that it was not caused by a terrorist act," said Marios Karoyian, a spokesman for President Tassos Papadopoulos.

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.

Two F-16 fighter jets were sent out shortly after the plane entered Greek air space over the Aegean Sea and 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. They also reported that there was no movement in the cabin.

Greek state television quoted Cyprus Transport Minister Haris Thrasou as saying the plane had decompression problems in the past.

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.

Rescue helicopters flew overhead and firefighting planes swooped low to extinguish some of the fires. 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 officials were also looking for the plane's two black boxes, two orange-colored devices that record data from the plane and the voices of the pilots in the cockpit. They are designed to survive crashes.

"The Helios flight that crashed in the Athens area left Larnaca and was headed for Athens. The causes of the crash are not known," government spokesman Theodoros Roussopoulos said.

Rescue workers and residents on the scene said they had not found any 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 back tail. The fuselage has been destroyed. It fell into a chasm and there are pieces. All the residents are here trying to help."

The head of the Greek airline safety committee, Akrivos Tsolakis, described it as the "worst accident we've ever had."

He speculated that there may have been a problem with the cabin pressure.

"There apparently was a lack of oxygen, which is usually the case when the cabin is de-pressurized," Tsolakis said.

Witnesses said they saw the plane being followed by the Greek air force jets when it crashed.

Greek radio and television stations reported that the air force pilots saw no movement in the cockpit of the plane before the crash. There were some reports the two pilots seemed to be unconscious.

"The plane crashed around 400 meters (yards) from homes in the area," said Miltiadis Merkouris, a spokesman for the Grammatiko municipality.

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.

Greek Prime Minister Costas Caramanlis canceled a holiday on the Aegean island of Tinos to return to Athens to deal with the crash. Cypriot President Tassos Papadopoulos also canceled a vacation.