North Sea operator Bond Offshore Helicopters has moved to defend itself from accusations of negligence, following a court ruling that a 2009 fatal crash involving one of its Airbus Helicopters AS332 Super Pumas might have been prevented.
Two pilots and 14 passengers were killed in the accident on 1 April 2009, when a catastrophic failure of the helicopter's main gearbox caused the rotor to separate and the AS332 (G-REDL) plunged into the North Sea 11nm (20km) northeast of Peterhead.
In his determination into the Aberdeen Fatal Accident Inquiry, Sheriff Principal Derek Pyle concluded there was a possibility that had Bond's engineers acted in accordance with the manufacturer's maintenance procedures, "the accident might have been avoided". However, he stresses that it is not proved beyond all reasonable doubt.
The inquiry heard that a Bond engineer had on 25 March discovered a metallic particle in the epicyclic chip detection unit on the Super Puma – the only clue to the impending failure of one of planetary gears inside the transmission.
However, investigations were not performed in line with the then Eurocopter's maintenance manual, which called for the removal of the epicyclic module for more detailed inspection. Although Bond engineers proceeded to examine both the AS332's main and epicyclic chip detectors after each sortie for a period of 36 flight hours following detection of the first particle, no further evidence of gearbox degradation was found before the helicopter's ill-fated journey between the Miller oil platform and Aberdeen airport.
Communications between Bond and the manufacturer covering the detection of the chip were also not correctly performed, leading to confusion between the parties about what process to follow. Additionally, the operator failed to analyse the nature of the metal particle.
Sheriff Pyle says "there can be no excuse" for failing to follow the procedures laid out in the inspection manual.
Although hearing conflicting evidence on the root cause for the failure of the second-stage planetary gear inside the epicyclic module, as investigations were hampered by the loss of key parts of the damaged component, Sheriff Pyle concludes that spalling – fatigue of the bearing surfaces causing release of metallic particles – was ultimately to blame.
Bond acknowledges the findings, while noting that nothing has been proved beyond reasonable doubt. It adds: "Additionally, [Sheriff Pyle] determined that even if we had followed the correct procedure, it is by no means certain that the gearbox would have been removed, as there may not have been sufficient evidence of particles to warrant its removal."
It accepts that mistakes were made through "honest confusion over telephone calls and emails", adding that "lessons needed to be learned, lessons have been learned and lessons continue to be learned".
Sheriff Pyle additionally recommends that helicopter manufacturers research the use of alternative materials to prevent spalling in gearboxes, to "thereby lessen the dependence upon maintenance procedures as the primary method of ensuring safety".