Two main theories that have now emerged about why the Chinese airliner suddenly nose-dived from a cruising height of 29,000 ft and crashed into a hillside.  Experts say that it was either due to a mechanical failure or sabotage, according to a BBC report.

The radar data shows the plane reaching maximum descent speeds of 31,000 ft per minute – or 157m per second.

"This is extremely excessive and not something we would normally see in any sort of flight. The aircraft would have been almost vertical," BBC cited Dr Sonya Brown, an aviation expert from the University of New South Wales, as saying.

Stating that there could be two reasons, Dr Brown said, “One is a catastrophic failure of the plane's horizontal tail – the part at the back which stabilises the plane and keeps it in line with the direction it's moving.

That could lead to the plane tipping over as it did. "That could be something mechanically caused – for example a runaway stabiliser," she said.

The other option that's increasingly being suggested among experts is sabotage.

She mentioned the Germanwings Flight 9525 crash in 2015, where a co-pilot crashed an Airbus carrying 150 people into the French Alps.

But she also pointed out that even then, the Germanwings aircraft only reached descent rates of 3,000-4,000ft per minute, compared to the 30,000 ft rate by which the Chinese flight plunged.

"So this is a significantly,different scenario – really extreme," Dr Brown said.

“Aircraft are designed to glide.., Even if all engines went out – the plane would slow down a little may be but it will just glide," she pointed out.

Experts are also baffled that about 7,000-8,000 ft from the ground, there was a slight upturn, the data shows. But then the plane continued its high speed plummet to the ground which could indicate sabotage.

Info about the pilots

There were three pilots on the plane, China Eastern officials disclosed on Wednesday. One of them was there as an observer to build up experience.

The captain had 6,709 hours flying experience, while the first and second officers had 31,769 hours and 556 hours respectively.

"From what we know, the performance of the three pilots had been good and their family life relatively harmonious," said airline spokesman Shangguan Xuemin.

He confirmed that typically, the airline deployed only two pilots on short-haul flights as per industry practice.

Black box

Meanwhile authorities have sent the cockpit recorder found at the crash site on Wednesday to a lab in Beijing for decoding. The black box was damaged by the impact of the crash, but the data inside appeared stable, officials said.

If the plane was deliberately crashed, the cockpit voice recorder will definitely give an indication of this. 

The flight data recorder is yet to be recovered. This second black box will contain information control settings, air data and other technological parameters related to mechanical issues.