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

An aviation expert said the alleged fatal error made moments before tragic Air India Flight 171 crashed would not have been an easy one to make due to fuel switch design

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.