A senior air accident investigator ruled out any suggestion of gearbox failure in a horror helicopter crash off Shetland.
Adrian Cope, a senior inspector for the Air Accidents Investigation Branch with 12 years expertise in aviation engineering, said the model of helicopter – the Super Puma – had a history of gearbox problems which have previously resulted in well-known offshore ditchings, and this had been a focus of their investigation.
A fatal accident inquiry is being heard virtually into the crash which happened just under two miles west of Sumburgh Airport on August 23, 2013.
Four offshore workers died on the day, while a fifth victim committed suicide four years later.
There was no evidence of a causal or contributory fault with the helicopter either before or during the accident.”
Survivors have described feeling “vibrations” on the aircraft moments before the crash, with one saying he heard a sound “like something tearing itself to bits”. He added: “At the time I thought the gearbox had gone.”
Mr Cope told the fourth day of the inquiry yesterday: “There was no evidence of a causal or contributory fault with the helicopter either before or during the accident.”
He added: “No evidence was found that would indicate the helicopter had not been maintained or certified in accordance with current regulations.”
Mr Cope said he was informed of the tragedy just hours after it happened and he flew north to Shetland the following day with colleagues.
They witnessed the recovery operation of the wreckage and also the cockpit voice recorder.
Mr Cope said: “We looked at a number of sources of evidence. We recovered all the records of the aircraft from the operator, the maintenance history, the flight recordings, the maintenance.
“There was nothing in these items which suggested there was an ongoing problem [with the helicopter].
“Once we recovered data from the flight recorder there was nothing to suggest there was an issue.”
There is a history of gearbox problems with this model of Super Puma Range”
Advocate depute Martin Richardson asked: “If it was suggested that there was a problem with the helicopter’s gearbox, how would such a problem manifest itself and how would you investigate that?”
Mr Cope replied: “There is a history of gearbox problems with this model of Super Puma Range. It is not a surprise that was the first thing that occurred to people as the cause of the accident.
“We looked at quickly … ruled it out.
“We looked at the wreckage, recovered the gearbox and investigated it internally. In previous occasions with gearbox failure it was badly damaged, as were the rotor blade. Not in this case.
“The recovered data showed the helicopter was flying as it should right up to the last minute.”
The victims were offshore workers travelling onboard a Eurocopter AS332 Super Puma helicopter belonging to CHC Helicopters when it crashed on approach to Sumburgh Airport.
The aircraft was flying workers off the Borgsten Dolphin oil platform to Aberdeen, but was about to make a refuelling stop in Shetland.
The co-pilot of the helicopter was yesterday praised for his “quick-thinking” in deploying flotation bags to keep it afloat and allow passengers to escape.
The actions of Captain Alan Bell were highlighted and it was said he “took the lead in assisting people to survive”.
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The inquiry has heard the helicopter crashed into the Atlantic Ocean west of Sumburgh with little warning beforehand to allow anyone to react, then overturned and quickly filled with water.
Mr Cope said of Capt Bell’s actions: “The co-pilot realised what was going to happen and armed the flotation bags.”
He said flight crew are given additional training about the knowledge of the helicopter they are flying over and above that of passengers.
This “awareness” ensured that Capt Bell’s “quick-thinking” ensured flotation bags were deployed – preventing it from sinking – as well as knowing about the deployment of liferafts.
Mr Cope said that while the chief pilot had suffered a serious back injury, the co-pilot was fit enough to deploy the flotation bags to keep the helicopter afloat, and then provide the knowledge to deploy the liferafts from which a number of passengers were rescued.
Mr Cope said: “His awareness and quick-thinking was really crucial. That kept the helicopter on the surface. If the helicopter was to sink it would be a dire situation. “He was aware of the liferafts.
The main problem [with surviving passengers] was trying to find the emergency release handles.”
The AAIB has recommended that the offshore industry incorporates automatic release of both floatation bags and liferafts on entering the water in the event of flight crew being unable to carry out the procedures.
Many passengers on the Super Puma flight were not aware how their emergency breathing systems operated.
There were three different re-breathing systems in operation at the time of the crash in 2013.
The first allows the passenger to blow a breath of air into the system prior to a ditching, and then use it once they are underwater.
The second has was a hybrid system which uses an “air bladder” in which there is a volume of air already available in the event of someone being submerged. This was the type in operation on the tragic flight.
The third system involves a “scuba-type” system giving air to people underwater. This system was recommended to be put in place across the industry and has been accepted across the UK.
New guidelines have since been introduced regarding emergency breathing systems – with the scuba system being the recommended rebreather across the industry.
The passengers who died on the day were: Sarah Darnley, 45, of Elgin; Gary McCrossan, 59, of Inverness; Duncan Munro, 46, of Bishop Auckland; and 57-year-old George Allison, of Winchester.
A fifth victim, Samuel Bell, from the London area, committed suicide four years later.
The inquiry continues and is expected to last four weeks.