Fatal helicopter crash caused by "catastrophic" gearbox failure

The helicopter which crashed in the North Sea last month killing all 16 men on board suffered a "catastrophic failure" in part of its main gearbox, according to an initial report.

The report, released last night by the Air Accidents Investigation Branch – part of the Department of Transport – concluded that a gearbox failure caused the main rotor to break away from the aircraft, and its tail boom to become severed from the fuselage. Its findings came in the same week as two other scares involving two helicopters flying over the North Sea.

Bond Offshore, which operates the Super Puma helicopter, has had their 10-year contract with BP suspended in wake of the fatality, pending the completion of a review. The report also issued an urgent safety recommendation, calling for "additional inspections" to be carried out on similar models.

The Super Puma ditched into the sea last Wednesday on its return from BP's Miller oilfield, claiming the lives of all 16 men – 14 passengers and two crew members – on board. The bodies of the victims have all been recovered and identified. Half of the victims came from north-east Scotland, seven from the rest of the UK, and one from Latvia.

The report said: "Examination of the wreckage indicates that the accident occurred following a catastrophic failure of the main rotor gearbox. This resulted in the detachment of the main rotor head from the helicopter and was rapidly followed by main rotor blade strikes on the pylon and tail boom, which became severed from the fuselage."

According to data found on the black box flight recorder, the co-pilot made a routine call at 1.54pm to say the arrival was scheduled for 2.14pm. Twelve seconds later, a may-day call was issued, which was followed by a similar call from the co-pilot. Air traffic controllers were unsuccessful in contacting the crew, and asked another helicopter to examine the Super Puma's last known radar position.

On Thursday, pieces of metal were seen coming from the exhaust of a EC225 Super Puma helicopter after it landed on Total's North Alwyn platform. The operators, CHC, said the helicopter, which was carrying two crew and 18 passengers, would be inspected by engineers before flying again. On Monday, another EC225 model – also operated by CHC – was forced to land on the Safe Caledonia rig after reporting a fuel problem on its way to Aberdeen from the Sedco 714 rig.

BP is currently using CHC and another operator, Bristows, for offshore flights while the Bond contract is suspended.