Indications the aircraft stalled aerodynamically imply the cockpit would have been filled with warnings alerting pilots to the danger, calling for them to tip the nose of the plane downwards in order to restore lift.

Airbus pilots say such warnings include an automated voice saying "Stall Stall" as well as an audible electronic signal and red warning light. In the 2009 crash of an Air France jet in the Atlantic, pilots appeared to ignore the warnings, prompting industry-wide efforts to reform pilot training.

Based on Jonan's data, there did not appear to have been a controlled descent in the case of QZ8501 and the aircraft appeared to have fallen rapidly before crashing into the sea, according to pilots and industry observers.

Bad weather in the area has been cited a possible factor in the crash, with the other aircraft close by at that time flying at altitudes of between 34,000 and 39,000 ft.

The investigators were looking into why this was the case, as well as QZ8501 pilots' reaction to the storms and clouds in the area, according to a source close to the investigation.

Industry experts say that the margin for error at higher altitudes is smaller than at take-off or lower down.

While the A320's systems usually prevent pilots from doing anything outside usual safe flight parameter, these protections can be disabled in some circumstances, handing control to the pilots and leaving it to manual flying skills.