The Cypriot airliner that crashed in Greece had lost cabin pressure and run out of fuel, investigators say.
A fire at the crash site made the identification of bodies difficult
The preliminary findings were reported by chief investigator Akrivos Tsolakis.
Autopsies have been conducted on all 118 bodies found at the crash site north of Athens. But three - including the captain's - are still missing.
Coroners say those on board the Helios Airways Boeing 737 were alive - though possibly unconscious - when it crashed on 14 August.
All but 11 of the victims were Cypriot and some 17 children are thought to have been on board.
A flight attendant is believed to have tried to take control of the airliner during its final moments.
The pilots of two Greek F-16s that shadowed the airliner just before the crash said they saw the co-pilot slumped over the controls and the captain was missing from the cockpit.
1999: Established as first independent airline in Cyprus
2000: First chartered flight
2001: First scheduled flight
Flies to UK, Strasbourg, Sofia, Athens, Dublin, Warsaw and Prague
Operates four Boeing 737 planes
"There 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," said the preliminary report released on Monday.
The catastrophic loss of cabin pressure would have exposed those on board to extreme cold and lack of oxygen.
Flight 522 had been heading for Athens en route to Prague when it lost contact with air traffic controllers, sparking a security alert before it crashed.
Mr Tsolakis said the plane's black box voice recorder indicated someone had repeatedly tried to send an emergency mayday signal.
A person wearing an oxygen mask was sitting in the pilot's seat for the final 10 minutes before the crash, the investigator said, adding that the tone of voice showed it was a man - either distressed or suffering from exhaustion.
But the emergency calls were not picked up by Athens Air Traffic Control, possibly because they were being transmitted on the wrong frequency.
Relatives have vented fury on Helios Airways, accusing the company of allowing an unsafe aircraft to take to the skies - a charge the Cypriot carrier denies.
Helios insists its plane was airworthy, but Greek television has reported that the airline's fleet has had a history of technical faults.
GREECE AIR DISASTER
1. 0900 [0700GMT]: Helios Airways Flight ZU522 leaves Larnaca bound for Prague via Athens
2. 0920 approx: Plane reaches cruising altitude of 35,000ft
3. 0937: Plane enters Greek airspace
4. 1007: Air traffic control unable to contact aircraft
5. 1030: Greek ATC issues "Renegade alert"
6. 1055: F16 fighter aircraft scramble
7. 1120: F16s intercept aircraft; pilots observed slumped over controls
8. 1205: Aircraft crashes near Grammatikos, 40km north of Athens