AAIB report finds identical ‘fatigue’ cracks led to North Sea Super Puma ditchings

THE identical cracks in the main gear shafts of two Super Pumas, forced to ditch in the North Sea earlier this year, both resulted from high cycle fatigue cracking near a weld, a new report by the Government’s Air Accident Investigation Branch has revealed.

And the agency’s latest bulletin has also confirmed an exclusive Scotsman report earlier this month which revealed that the warning of a lubrication system failure on the CHC-operated Super Puma EC225 which ditched off Shetland in October was a false alarm - identical to the scenario in the ditching in May involving a Bond-operated Super Puma EC225

The AAIB is recommending that the European Aviation Safety Agency orders Eurocopter, the French manufacturer of the aircraft, to review the design of the main gearbox emergency lubrication system on the EC225 Super Puma “to ensure that the system will provide the crew with an accurate indication of its status when activated.”

The report states that the failure of the bevel gear vertical shaft on both aircraft occurred as a result of “high cycle fatigue” in the area of an “electron beam” weld is used to join the main bevel gear wheel and the vertical shaft .

And it continues: “The failure is thought to be as a result of the shaft bending (flexing) as it rotates.”

The bevel gear vertical shaft fitted to the Super Puma involved in last month’s ditching had operated for only 167 flying hours before the incident, while the shaft fitted to the helicopter involved in the May emergency had operated for 3,845 flying hours.

The report states: “The investigation has not identified the root causes of the failure of the bevel gear vertical shafts fitted to (the two helicopters). It is possible that the failures occurred for different reasons..

“The investigation is currently seeking to confirm the material properties and the in-flight dynamic loads.