Lion Air flight 610 fell 1479m in 21 seconds

Data from a fatal flight out of Jakarta suggests it could have fallen nearly 1500m in a matter of seconds.

Lion Air flight JT610 crashed into the sea shortly after taking off from Jakarta. The plane was a new Boeing 737 and had only logged 800 hours in the air.

Both pilots were experienced and between them had spent 11,000 hours flying.

The plane made unpredictable changes in altitude shortly before the crash, before plunging dramatically into the sea, reports.

It's believed the plane dropped from an altitude of 1479m in just 21 seconds. 

An expert in airplane safety said FlightRadar24 data suggesting a descent of 9400m per minute was "barely believable" due to how fast it was.

"This thing really comes unglued," said John Cox, who runs consulting company Safety Operating Systems, told Bloomberg.

A normal flight would descend for landing at a rate of 450m to 600m per minute.

Attention is now turning to what would have caused such a new plane, flown by experienced pilots, to crash so suddenly.

Aviation analyst Captain John Nance told The AM Show on Tuesday there's not much on a 737 that can make it crash.

"Back in the days when you had aviation gasoline in airlines, DC7 and so on, you could have a wing blow off because something sparked on an otherwise empty tank," he said.

"We know this can happen in a cavernous tank in a 747... but that's not a thing that can happen to a 737 these days for many different reasons."