Nov 252011

Main rotor head of G-REDL is recovered

Oil & Gas UK says that it welcomes the Air Accidents Investigation Branch (AAIB) report published on 24 November on the tragic crash of helicopter Flight 85N which took place off the Aberdeenshire coast on 1 April 2009.

The accident occurred whilst the helicopter was operating a scheduled passenger flight from the Miller Platform in the North Sea, to Aberdeen. Whilst cruising at 2,000 ft amsl, and some 50 minutes into the flight, there was a catastrophic failure of the helicopter’s Main Rotor Gearbox (MGB). The helicopter departed from cruise flight and shortly after this the main rotor and part of the epicyclic module separated from the fuselage. The helicopter then struck the surface of the sea with a high vertical speed.

Debris from a helicopter, two life rafts and eight people wearing survival equipment were observed within the area. A fast rescue boat crew, however, found no signs of life.

An extensive and complex investigation revealed that the failure of the MGB initiated in one of the eight second stage planet gears in the epicyclic module. The planet gear had fractured as a result of a fatigue crack, the precise origin of which could not be determined. However, analysis indicated that this is likely to have occurred in the loaded area of the planet gear bearing outer race.

A metallic particle had been discovered on the epicyclic chip detector during maintenance on 25 March 2009, some 36 flying hours prior to the accident. This was the only indication of the impending failure of the second stage planet gear. The lack of damage on the recovered areas of the bearing outer race indicated that the initiation was not entirely consistent with the understood characteristics of spalling (see The possibility of a material defect in the planet gear or damage due to the presence of foreign object debris could not be discounted.

Robert Paterson, Oil & Gas UK’s health and safety director, says: “We remember, first and foremost, all those who lost their lives in this tragic accident and give our sincerest respects to their families, friends and work colleagues. “

Following the two major helicopter incidents in 2009 the industry, together with the relevant regulators and trade unions, established the Helicopter Task Group to drive immediate improvements in helicopter safety. Its agenda is now being taken forward by the Step Change in Safety Helicopter Safety Steering Group. “While the AAIB report confirms that neither the actions of the crew nor the weather were factors in the accident and that the helicopter maintenance regime satisfactorily complied with existing regulations, it does make 17 recommendations. A number of these were highlighted in the AAIB’s interim reports and have already been addressed and applied by the helicopter operators in the two years since the accident. The new recommendations focus on additional monitoring of technical components and the Helicopter Safety Steering Group will conduct its own detailed review of these recommendations and will focus on monitoring their implementation.”

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