Watch: Role of plane fuel switches explained

The preliminary report into the Air India crash in June has found that both fuel control switches, which are used to turn the engines off, were at one point moved to the cut-off position.

Audio from the cockpit detailed in the report suggests confusion between the two pilots: in a voice recording, one is heard asking his colleague why he "did the cut-off" - the other pilot replies he did not do so.

As experts continue to try and understand how the switches came to be moved, the BBC's International business correspondent Theo Leggett explains their role, and how shifting them is a two-stage process.