The aircraft departed Larnaca, Cyprus at 9:07am local time for a scheduled passenger flight to Athens, Greece. Shortly after departure, at 9:37am, the aircraft entered Greek airspace, and over the next 30 minutes, the crew failed to make contact with Greek air traffic control. At 10:20am, Greek air traffic controllers contacted their Cypriot counterparts, who reported that the flight crew had reported a problem with the 737′s air conditioning packs shortly before entering Greek airspace.
Subsequent attempts to establish contact with the flight crew failed, and at 10:55am, two Greek F-16 fighter jets were scrambled to intercept the stricken airliner. The fighter jets established visual contact with the 737 at 11:20am over the Aegean Island of Kea, and subsequently reported that the Captain was not in the cockpit, the first officer was unconscious, slumped over the flight controls, and that the cabin oxygen masks appeared to be deployed. The F-16 jets continued to follow the aircraft as it started descending and, at 12:05pm local time, crashed into arid, mountainous terrain about 19 miles north of Athens’ Eleftherios Venizelos Airport.
The investigation shows that the cabin pressure regulation valve (located aft the fuselage) would have remained opened. The crew would have set this valve into manual control (so, open), letting the aircraft at atmospheric pressure. The crew would have fainted before being aware of the problem. The aircraft flew until it ran out of fuel.