The thinking now is that there was no sudden catastrophic decompression on Helios Flight 522, but perhaps something more in line of a very slow leak, maybe from a bad door. Or the compressor that makes the thin air piped in from outside breathable may have malfunctioned. They're also wondering why the plane's air conditioners had to be repaired five times in two months. There were also electrical problems caused by the overheating generated by poor ventilation. People had been saying all along that it couldn't have been sudden decompression or the F16 pilots wouldn't have been able to see through the windows -- they'd have been iced over like the Payne Stewart plane.
The cockpit recording device did record voices and, understandably, they're not releasing at this time, as it's said to contain cries for help, along with heavy breathing. The voice is believed to belong to flight steward Andreas Prodromou. Prodromou tried to land the aircraft and was occupied in doing this when the plane ran out of gas. His blood was in the cockpit, and he'd motioned to an F16 pilot that he was going to make the attempt. What a guy.
This is hard for me to understand, so someone correct me if I'm wrong, but there were three types of emergency oxygen on board. The kind for the pilots drew from some line with a valve, the kind for the cabin crew was a portable chemical exchange sort, and the type used for passengers had a 15-minute supply. I can only guess that the cabin crew's supply is set up as it is because they're expected to move around, while the pilots and passengers would be expected to be seated.
There are still three remains missing, including the pilot. The pilot was not in the cockpit, and may have commited the very bad error (from the Pilots' Forum at least) of getting up out of his seat to check on things, perhaps the oxygen line. If it was a slow leak and the cockpit's supply of emergency oxygen wasn't working properly, this might be more understandable. His thinking would have been muddy. His last words on the radio were, "It's OK."
Flight International has published the sequence of events given them by Cpt. Akrivos Tsolakis, head of the Greek Air Accident Investigation and Aviation Safety Board, as follows:
09:05: Take off from Larnaca.
09:11: Pilots report air conditioning problem.
09:1?: Climbing through 14,000ft (4,270m), the cabin altitude warning alert activates and is not cancelled by the pilots for the duration of the flight. It self-cancels when the aircraft eventually descends through 10,000ft.
09:16: Last radio communication with pilots as aircraft climbs through 22,000ft.
09:24: Aircraft adopts cruise at flight level (FL) 340 (34,000ft/10,360m), probably flying on autopilot with direction from the pre-programmed flight management system (FMS).
09:35: Cyprus ATC tells crew to contact Athens as it approaches the flight information region (FIR) boundary.
09:37: aircraft enters Athens FIR near Rhodes. Radar picture shows aircraft on time and on track at FL340.
10:07: Athens airport tries to contact the inbound aircraft because it should have begun its descent. No reply.
10:20 (approx): Aircraft enters holding pattern at the VOR on Kea island south east of Athens, probably still on autopilot/FMS.
10:25: Athens airport contacts search and rescue services.
10:30: Minister of Defence and Greek air force alerted.
10:55 (approx): Two Lockheed Martin F-16 fighters scrambled.
11:25 (approx): F-16s formate within a metre of the 737, report no captain in seat, copilot slumped on controls, two other people in cockpit, passenger oxygen masks deployed, no movement in cabin.
11:50:45 Aircraft begins descent, leaving holding pattern flown by the air steward, a student pilot with only a few hours’ experience on light aircraft. It is believed he maintained consciousness by using the portable oxygen equipment stowed in the cabin. The aircrad turns right out of the hold, passing over Evvoia island and the Aegean Sea to the north east of Athens.
11:??: Engines flame out for lack of fuel as the aircraft descends through 7,000ft. Aircraft turns left toward Athens airport.
12:04: Aircraft crashes among hills at Grammatikos.
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