An initial report on a helicopter crash that killed 16 people off the Scottish coast has found the aircraft suffered a catastrophic failure in its main gearbox.
The report by British air accident investigators found that the failure - which they said was not yet fully understood - caused the helicopter's main rotor to break away from the aircraft and its tail boom to become severed from the fuselage.
There was also a rupture in the helicopter's right-hand engine casing, the investigators said.
The Super Puma helicopter carrying 14 passengers and two crew crashed into the North Sea on 1 April as it was returning to the mainland from a BP oilfield off the northeast coast of Scotland.
The investigators recommended that the helicopter's manufacturer, Eurocopter, should urgently carry out "additional inspections" on other Super Pumas, which are commonly used to ferry staff to oil rigs in the North Sea.