The new leader of the US Federal Aviation Administration said the deadly crash of an Air India Boeing Co. 787 jet last month was unlikely to have been caused by a mechanical issue with the plane or inadvertent movement of the aircraft’s fuel control switches.

The head of the Federal Aviation Administration said Thursday the fatal crash of an Air India Boeing 787 does not appear to be caused by a mechanical issue or inadvertent movement of the fuel control unit.

With 260 casualties and only one surviving passenger, the Air India 171 crash is one of the deadliest aviation incidents in recent history — and so far it’s proving to be one of the most frustratingly opaque.