But the only record of all cockpit conversations - the planes' voice recorders - may not have survived, said Mr Learmount.

BBC: Cockpit drama of doomed planes

But last time I checked, big companies like Sony, Panasonic, Olympus, RCA and others were still profitably making digital voice recorders.

FORBES: Video Killed the Radio Star, But Smartphones Did NOT Kill the Flip Cam

The investigation will include scrutiny of the flight and voice data recorders, it said.

CNN: Report: Stray jet's pilots were on laptops