An official report on the world’s deadliest aviation accident in a decade, seen by CNN, has answered one key question – but raised others.

In the cockpit voice recording, one of the pilots is heard asking the other why he "did the cut-off", the other pilot replied that he didn't.

Preliminary findings into last month’s Air India plane crash suggest the aircraft’s fuel control switches were turned off, causing a loss of engine thrust shortly after takeoff.