Reuters International

Bergen, 20160429: A helicopter has crashed west of the Norwegian city of Bergen with 13 people on board. NTB Scanpix/Torstein Boe/via REUTERS

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OSLO (Reuters) - An investigation into the cause of a fatal North Sea helicopter crash is focusing on the parts of the aircraft that connected the rotor blades to the main body of the helicopter, investigators said on Friday.

An Airbus H225 Super Puma helicopter ferrying passengers from a Norwegian oil platform operated by Statoil crashed on April 29, killing all 13 people on board.

Since then the helicopter model, a workhorse of the oil industry, has been grounded for commercial flights in Norway and Britain. Investigators have ruled out human error, saying that the crash was caused by a technical fault.

On Friday a preliminary report by the Norwegian Accident Investigation Board said it was focusing on a specific section of the aircraft.

"The (investigation board) is currently focusing on the examination of the MRH (main rotor head) suspension bar assembly, the main gearbox and the main rotor head," it said.

The report did not say whether the problem was attributable to design, production or maintenance issues. Design and production are the responsibility of Airbus Helicopters, while maintenance is handled by the operator, CHC Helicopter.

On May 4 European safety regulators ordered checks on all H225 Super Pumas, including three metal struts that help to connect the rotor assembly to the helicopter.

The Super Puma has been in operation since the 1970s and there are 800 in operation worldwide.

Any conclusion over the cause of the crash would be premature at this stage, investigators said.

"It is very complicated work and we have a lot of work ahead of us," investigation leader Kaare Halvorsen told a news conference.

The accident happened suddenly, Friday's report said. "Everything appeared to be normal until a sudden, catastrophic failure developed in 1-2 seconds," it said.

The helicopter was cruising at 2,000 feet when the main rotor head and mast suddenly detached, it said.

"The helicopter impacted on a small island and caught fire. The main wreckage thereafter ended in the sea where it came to rest at a depth of 1-9 metres. The accident was not survivable."

(Reporting by Gwladys Fouche; Editing by David Goodman)

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