The sudden movement of engine fuel switches has taken centre stage in the investigation of the Air India Boeing Dreamliner crash that killed 260 people in June, the world's worst aviation disaster in a decade.

India’s Directorate General of Civil Aviation stated the directive would apply to Boeing 787 Dreamliners and select Boeing 737 variants and that airlines must complete inspections and submit their findings to the regulator by July 21.

A preliminary investigation into last month's Air India crash that killed 260 people reveals cockpit confusion before the Boeing Dreamliner went down. The report from India's AAIB has sparked media speculation but identified no cause.