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

However, Greece's government and military officials refused to comment on the reports until the end of an investigation, heightening speculation about what caused the mysterious crash of the Helios Airways flight from Larnaca, Cyprus, to Athens.

In London, the British pilots' union urged Greek authorities to release preliminary findings for the sake of the aviation industry.

"There have been several apparently conflicting reports and a number of statements that just don't add up," Capt. Mervyn Granshaw, head of the British Airline Pilots' Association, said without elaborating. "There is a concern in our industry to learn, as quickly as possible, what happened. ... If there is too much delay, the speculation will increase."

From the first, the Greek government has said the cause of the crash was likely technical failure and not terrorism. But with so many unanswered questions, industry experts said Wednesday it was too soon to tell.

"Until they can absolutely rule it out, they've got to consider a terrorist act or some sort of sabotage as a potential factor," said Richard Healing, former member of the National Transportation Safety Board.

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Two Greek air force F-16 jets were scrambled after the Helios flight lost radio contact flew by the airliner over the Aegean Sea. The F-16 pilots reported seeing the pilot's seat empty and the co-pilot slumped over the controls, possibly unconscious, according to the Greek government.

The government also said the F-16 pilots saw two unidentified people in the cockpit trying to regain control of the plane. Authorities have not released the fighter pilots' account of the passenger jet's final 23 minutes of flight or how it crashed.

But Greek state-run and private media, quoting anonymous defense ministry officials, have said the F-16 pilots also saw someone in the cockpit — probably a man — take control of the plane as it flew in a gradually descending holding pattern, apparently on autopilot, at about 37,000 feet near Athens airport.

That person then banked the plane away from Athens, lowering it first to 2,000 feet and then climbing back up to 7,000 feet before the plane apparently ran out of fuel and crashed.

For those maneuvers to happen, someone who knew how to work the airplane had to have been in control, said Paul Czysz, emeritus professor of aeronautical engineering at St. Louis University. The lack of air traffic control contact also was suspicious, he added.

"Obviously, he didn't want to contact the tower," he said. "It's happened before."

On Oct. 31, 1999, the pilot of an EgyptAir flight from New York to Cairo apparently directed the plane into the Atlantic Ocean off the coast of Nantucket, a crash that killed 217 people.

Many aviation experts believe a suicidal pilot also caused the Dec. 19, 1997 crash of a Singapore SilkAir Boeing 737-300 near the Indonesian city of Palembang, killing all 104 aboard. The Indonesian government concluded they didn't know what caused the crash.

According to the media accounts, the person flying the plane made an effort to land in the mountainous terrain. By that time, the plane had been flying for about an hour and a half beyond its scheduled arrival time — and twice as long as a normal flight from Cyprus to Athens.

The reports also said the person at the controls was likely 25-year-old flight attendant Andreas Prodromou, whose relatives have said he had a pilot's license. Chief investigator Akrivos Tsolakis has confirmed someone apart from the pilot and co-pilot on board was qualified to fly an aircraft, but would not elaborate.

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The Helios Airways flight was declared "renegade" when it failed to respond to radio calls shortly after entering Greek airspace, clearing the way for Prime Minister Costas Caramanlis to order the F-16s to shoot it down if it was deemed a threat to populated areas.

But government spokesman Theodoros Roussopoulos insisted there was no such threat, and that Caramanlis did not consider that option.

Magnus Ranstorp, director of the Center for the Study of Terrorism and Political Violence at the University of St. Andrews in Scotland, said it was a close call.

"There hasn't been any situation like we saw recently with the Greek case where you were so close to taking this decision," Ranstorp said.

A team of six medical examiners has been trying to determine whether anything on board the plane made the passengers and crew lose consciousness before the crash.

Autopsy results on 26 bodies identified have shown passengers and at least two crew members — including the co-pilot — were alive, but not necessarily conscious, when the plane went down.

Investigators are also looking into claims the plane had technical problems in the past.

Tsolakis, the chief investigator, said the Helios plane's flight data recorder, which has been sent to Paris for decoding, could provide essential clues.