A preliminary assessment in last month’s disaster focusing on fuel being cut to both engines only deepened the mystery for people grieving loved ones.

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.

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