EgyptAir Flight 990 investigators are currently relying on three sources for evidence of what happened: Radar reports of the aircraft's flight in the last minutes and the airliner's two "black box" recorders - one for flight data and the other for the voices in the cockpit.

Some 40 minutes into the transatlantic flight and everything appeared normal.

Jim Hall, head of the US's National Transportation Safety Board, charged by the Egyptian government with carrying out the investigation, said: "The data show an uneventful flight, cruising in level flight at 33,000 feet.

By this point, the aircraft has reached its standard transatlantic altitude and the crew had activated the autopilot system for navigation across to Europe and North Africa.

According to the flight data recorder (FDR), the autopilot disconnected less than a minute later. While this is an unusual procedure, an autopilot can be easily overridden by a pilot at any moment if the crew wants to take control of the aircraft.

Ten seconds later, both radar returns and data from the FDR reveal that the engines appeared to throttle down and there was an overall reduction in the amount of thrust.

By 01:50 the plane had started its descent.

Flight 990's passengers experience complete weightlessness as the dive becomes steeper.

The airliner accelerates to around 0.86 the speed of sound.

The aircraft's master warning system activates and the engine monitors warn of low oil pressure. Records appear to show that the crew ignored the warnings.

It takes the aircraft less than 20 seconds to dive 12,000ft. Seconds later, as the aircraft descends below 20,000ft, the start levers on both engines switch from run to cut-off, shutting down the engines.

Boeing has said that the engines could only have been intentionally shut down.

At about 1:50.30, the aircraft appears to pull out of its nose dive.

Radar traces show that the aircraft then began to stabilise and gain height, reaching some 24,000ft over the next minute.

However, considering that the aircraft had entered the steep dive at extremely high speed, most of the height could have been gained by the aircraft's forward momentum.

There is no evidence that the engines were throttled up.

Despite the radar images showing this gain in height, the aircraft reaches a peak, rather like a ball having been thrown in the air, and re-enters a steep and final dive to the sea.

Jigsaw puzzle

Air accident experts are continuing to extract information from the flight data recorder and may even feed it into a Boeing cockpit simulator to try and re-enact the final moments in the cockpit.

But the most crucial job they have at the moment is synchronising the cockpit voice recordings with the FDR material.

The NTSB is continuing translation work, aided by Arabic speakers with knowledge of Egyptian idiom, but already there are several significant pieces of the jigsaw which have to be matched to events.

NTSB officials have yet to explain the sequence or timing of events on the voice recorder but they have released some of the key features to the media.

Investigators say that the opening and closing of a cockpit door can be heard, following by a voice believed to be reciting the Shahada, the Islamic affirmation of faith.