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Gearbox cracks the cause of helicopter ditchings

FATIGUE cracks in the main gearbox have been blamed for the ditchings of two North Sea helicopters.

Air accident investigators have today published the findings of their probe into two separate incidents in 2012, which both involved EC225 helicopters carrying oil workers. No one was seriously injured in either ditching.

In May 2012, the crew of an EC225 Super Puma flying east of Aberdeen was forced to make an emergency landing in the North Sea following a loss of oil pressure in the main rotor gearbox and the apparent failure of the emergency lubrication system to kick in.

In October that year, a second EC225 Super Puma ditched off the Shetland islands in identical circumstances.

A report by the Air Accidents Investigation Branch has concluded that the "loss of oil pressure in both helicopters was caused by a failure of the bevel gear vertical shaft in the main rotor gearbox, which drives the pumps".

The report continues: "The shafts had failed as a result of a circumferential fatigue crack in the area where the two parts of the shaft are welded together...the emergency lubrication system operated in both cases, but the system warning light illuminated as a result of an incompatibility between the helicopter wiring and the pressure switches."

A number of safety recommendations relating to the EC225 gearbox flaws have already been issued in the aftermath of the 2012 incidents, but the AAIB have also called for improvements to emergency checklists, life-rafts and the crash position indicator, which alerts rescuers to the location of a ditched aircraft.

The 2012 incidents are among a string of offshore helicopters crashes and ditchings which have led to tougher safety regulations.

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