According to Greek military radar data, Flight 804 veered off course shortly after entering the Egyptian airspace. At an altitude of 37,000 feet (11,000 metres), the aircraft made a 90-degree left turn, followed by a 360-degree right turn, and then began to descend sharply. Radar contact was lost at an altitude of about 10,000 ft (3,000 m).
On 20 May, France's Bureau of Investigations and Analysis (BEA) in France confirmed that Aircraft Communications Addressing and Reporting System (ACARS) messages contained the following data.
00:26Z 3044 ANTI ICE R WINDOW
00:26Z 561200 R SLIDING WINDOW SENSOR
00:26Z 2600 SMOKE LAVATORY SMOKE
00:27Z 2600 AVIONICS SMOKE
00:28Z 561100 R FIXED WINDOW SENSOR
00:29Z 2200 AUTO FLT FCU 2 FAULT
00:29Z 2700 F/CTL SEC 3 FAULT
No further ACARS messages were received, and contact with the aircraft was lost four minutes later at 00:33 UTC. The data, confirmed by BEA indicates that smoke may have been detected in the front of the airliner - in the front lavatory and the avionics bay beneath the cockpit. Smoke detectors of the type installed on the aircraft can also be triggered by water vapour in the event of a sudden loss of pressure inside the cabin. The three windows mentioned in the data are cockpit-windows. The flight control unit (FCU) is a cockpit-fitted unit that the pilot uses to enter instructions into the on-board flight computer. The spoiler elevator computer number 3 (SEC 3) is the computer that controls the spoilers and elevator actuators.Two pilots interpreted the data as evidence of a possible bomb.
Smoke or condensation was detected in one of the aircraft's lavatories and in the avionics bay shortly before it disappeared from radar. No emergency call was received by air traffic control. Experts are investigating the cause of the disaster.
By 21 May, SAR vessels began recovering small pieces of debris, including seats, body parts and both interior and exterior components..