'It just doesn't fall out of the sky like that'

As the families of the 239 people who had been on board MH370 continued their agonising vigil on Sunday, the world was no closer to an answer to what happened to the missing Boeing 777-200.

But what became clearer was that some usual factors involved in aircraft accidents could be ruled out.

Experts insist that the weather conditions over the South China sea that day - benign - are unlikely to have caused the plane any distress.

If there had been a mechanical fault in the aircraft, others argue, why had the pilots not issued any distress calls?

Another cause for concern: The point at which the plane vanished.

Said CNN's aviation expert Richard Quest: "It was two hours into the flight - this would have been classed as the 'cruise portion of the flight'.

You break down the flight into taxi, take-off, climb out and then cruise. So in that particular point of the flight, this is the safest part, nothing is supposed to go wrong. The aircraft is at altitude on auto-pilot, the pilots are making minor corrections and changes for height as the plane burns off fuel - the plane will be going higher and higher - so this is extremely serious that something happened at this point in the flight."

The age and condition of the aircraft is another issue that has experts puzzled.

Said Mr Quest, on the 12-year-old 777-200 which had passed a stringent safety inspection just a week earlier: "It's not a particularly old aircraft. Malaysia has 15 777-200s in its fleet, it's an extremely experienced operator of this type of aircraft.

"It's a very reputable airline with a very good safety record."

SUDDENLY LOST POWER?

Could the aircraft have suddenly lost power?

That's unlikely, said Mr Greg Feith, a former investigator with the US National Transportation Safety Board (NSTB).

He said the pilots should have been able to report in, even if power on the aircraft had failed.

"The airplane by certification has to have battery back-up power - they still have to be able to utilise certain flight instruments and communication tools to complete the flight safely.

"So you could lose all the generators, you could have both engines out, but the battery back-up - which will work only for a certain time - is intended for emergency situations."

Mr John Goglia, a former board member of the NTSB, said the lack of a distress call suggested that the plane either experienced an explosive decompression or was destroyed by an explosive device.

"It had to be quick because there was no communication," Mr Goglia said.

Added Mr Feith: "If you have a high-altitude pressurisation problem, catastrophic decompression, the time of useful consciousness (the time a pilot can operate with an insufficient oxygen supply) in the 30,000-40,000-feet range is a matter of seconds."

Despite this, several experts were quick to suggest that the 777-200's safety record makes that scenario unlikely.

Said aviation expert Jim Tilmon: "The only fatality has been from the Asiana crash in San Francisco (last year). There's been one other 777 that had some problems, but no one was hurt. This is really a shock in lots of ways."

Echoing that view, a former Malaysia Airlines pilot who works for a rival airline said: "The Boeing 777 doesn't just stall like that. It is one of the safest planes out there. It doesn't just fall out of the sky like that."

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