The initial report into a Helios jet which crashed mysteriously killing all 121 people on board suggests that an unknown man was wrestling with the controls as the plane ploughed into a mountainside in Greece.

Investigators said today that the plane suffered a catastrophic loss of cabin pressure which had apparently incapacitated the two pilots. It eventually ran out of fuel and crashed.

Chief investigator Akrivos Tsolakis wrote: “There is proof ... that a person wearing an oxygen mask was sitting in the pilot’s seat for the final 10 minutes (before the crash).

“This person twice attempted to send a mayday signal, in a fashion that could not be picked up by any station. The tone of voice showed that it was a man, either distressed or suffering from exhaustion."

Mr Tsolakis presented his initial findings to the Greek Transport Ministry following the analysis of flight recorders and autopsies on all 118 bodies recovered from the site. Three bodies have not been found.

Helios Flight 522, flying from Larnaca, Cyprus to Athens, crashed near the village of Grammatiko, 40 km (25 miles) north of Athens on August 14, in Greece’s worst air disaster.

"That are indications of technical problems in the pressurisation system ... There is proof that the engines of the plane stopped working because the fuel supply was exhausted, and that this was the final cause of the crash," he said in the report.

The man who attempted to steer the plane is believed to be flight attendant Andreas Prodromou, whose blood was reportedly found in the remains of the cockpit, and who had received flight training in the past.

A former chief mechanic at Helios has revealed that the plane lost cabin pressure during a December flight after a door apparently was not sealed properly.

On the day of the crash, two Greek air force F-16 fighter planes were scrambled to intercept the flight shortly before the accident. They reported seeing the co-pilot slumped over the controls, apparently unconscious, and said that the pilot was not in his seat. They also reported seeing oxygen masks dangling in the plane’s passenger cabin.

Yesterday, Public Order Minister Giorgos Voulgarakis repeated government assurances that the plane had not been shot down.

"If this incident had taken place during the Olympics, the chances of it being shot down would have been extremely high," Mr Voulgarakis conceded in a newspaper interview.

A Helios spokeswoman in London said today: "The Greek accident is in the hands of the investigators and we are co-operating with them."

Helios Airways is continuing its flights to and from UK airports, but has suffered a litany of technical problems. The day before the Greek crash, a Helios’ pilot radioed that he was having trouble with his aircraft flaps but the plane was able to land safely at Birmingham airport. Last week another Helios plane en route for Luton airport was diverted to Stansted airport where it landed safely after the crew again reported a flaps problem.

This morning, around 200 Irish passengers remained stranded in Cyprus after a Helios flight was cancelled yesterday. A spokeswoman for the Irish Department of Foreign Affairs said: "It is a Helios flight and our embassy in Cyprus has been in contact with the airport and officials. All of the passengers will be brought home today."

She added: "There have been no official reports to our embassy officials in Cyprus that any of the waiting passengers has been taken to hospital or taken ill."

The delay is believed to be linked to the difficulties arising out of the fatal crash. The passengers, who have been waiting at Larnaca, have been informed they will be flown home this evening.

Meanwhile, the British airline pilots’ union Balpa reassured passengers today that UK aviation safety was "second to none", in a move meant to curb anxiety followed the Helios disaster and other recent crashes.

Balpa chairman Captain Mervyn Granshaw said: "Understandably, at this time, some people are worried about flying, with three separate incidents in recent weeks. But in Britain we have the most stringent tests and regulation, of both aircraft and flight crew.

"Pilots have to undergo rigorous twice-yearly technical competency as well as medical checks, and any failure of any test would result in a pilot being grounded and his or her licence invalidated."

Capt Granshaw went on: "If any pilot was thought to be less than thoroughly professional, he or she would be sacked. Any incompetent pilot would soon be identified and shown the door.

"The Civil Aviation Authority (CAA), the UK airline regulator, is very rigorous too. So any problematic UK airline would have their air operator certificate withdrawn and this would end their ability to operate flights."

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