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

The US Federal Aviation Administration has issued a notice to its international counterparts that fuel control switches in Boeing aeroplanes like the Dreamliner involved in last month’s fatal Air India crash do not pose a safety issue.

Investigators released a preliminary account of the crash, describing how the plane struggled after its fuel supply was cut.