A preliminary report into the deadly crash of an Air India jetliner in June is expected to be released by Friday, three sources with knowledge of the matter said, with one adding the probe had narrowed its focus to the movement of the plane's fuel control switches.

The London-bound Boeing 787 Dreamliner, which started losing height after reaching an altitude of 198 meters, crashed moments after takeoff from Ahmedabad, India, killing 241 of the 242 people on board and others on the ground.

The investigation into the Air India crash is focusing on the movement of the engine fuel control switches following an analysis of the 787's flight and voice data recorders, along with a simulation by Boeing of the aircraft's final moments, one of the sources said.