Dehradun, July 20 -- The Aircraft Accident Investigation Bureau's (AAIB) preliminary report into the May 8 helicopter crash in Uttarkashi district of Uttarakhand revealed that the accident was caused by an overhead fibre cable that struck the helicopter's main rotor blade during emergency landing. The Bell 407 helicopter, operated by Aerotrans Services Pvt Ltd, was en route from Kharsaili in the Yamunotri Dham to Jhala helipad in Gangotri Dham when it plunged into a gorge about 200-250 metres deep in the Gangnani area of the district, killing six people and grievously injuring another onboard. According to the AAIB report, released on Saturday, the chopper was airborne for about 20 minutes before it began descending from its cruising altitu...