Investigators have revealed it took just 30 seconds for a routine helicopter flight to turn into a tragic disaster.
The CHC-operated Super Puma plunged into the sea off Shetland because its crew failed to monitor cockpit instruments properly.
Sarah Darnley, 45, from Elgin, Gary McCrossan, 59, from Inverness, Duncan Munro, 46, from Bishop Auckland, and George Allison, 57, from Winchester, all died in the accident in August 2013.
Twelve other offshore workers and the pilot and co-pilot survived. The wife of one of the passengers who escaped has revealed she had a “gut instinct” he was on board when she heard about the crash.
The Air Accidents Investigation Branch (AAIB) has ruled the crew of the doomed aircraft did not “adequately monitor” cockpit instruments during its approach to Sumburgh on Shetland.
No evidence of a fault with the CHC-operated helicopter was found either before or during the flight.
Investigators also revealed the co-pilot said after the accident that he did not feel he had received training on the specific duties of the pilot not flying (PNF) in terms of monitoring the progress of an approach.
The Super Puma AS332 L2, carrying 16 passengers and two crew, plunged into the sea at 5.17pm on August 23, 2013.
It had left the Borgsten Dolphin semi-submersible drilling platform in the North Sea and was en route for a refuelling stop at Sumburgh Airport.
Sarah Darnley, 45, from Elgin, Gary McCrossan, 59, from Inverness, Duncan Munro, 46, from Bishop Auckland, and George Allison, 57, from Winchester, all died in the accident
The AAIB’s report on the crash, published yesterday, concluded that in the latter stages of the approach, there was a period of about 30 seconds when the flight instruments were “not adequately monitored” and the helicopter’s airspeed continued to reduce “unchecked”.
It also provided details for the first time about how the passengers died – one in the liferaft from a chronic heart condition, likely to have been exacerbated by the stress of the evacuation, and the three others by drowning.
One of them – who had tried to use the emergency breathing system – got trapped in the cabin, while another managed to escape but did not survive.
The third suffered a head injury during impact.
The report said the lack of monitoring meant a reduction in air speed went unnoticed by the pilots until it was too late, leaving the helicopter in a “critically low energy state”.
Identifying these as the two “causal” factors, it concluded: “The helicopter’s flight instruments were not monitored effectively during the latter stages of the non-precision instrument approach.
“This allowed the helicopter to enter a critically low energy state, from which recovery was not possible.
“Visual references had not been acquired by the minimum descent altitude and no effective action was taken to level the helicopter, as required by the operator’s procedure for an instrument approach.”
According to the report, the co-pilot stated after the crash that he did not feel he had received training on the specific duties of the Pilot Not Flying (PNF) in respect of how to monitor the progress of an approach, or of how to monitor the other pilot.
Additionally, he considered that he had not received guidance as to when as the PNF he should look outside during an approach to acquire the visual references required for landing.
As well as the causal factors, a number of “contributory” factors were highlighted, including the operator’s lack of a “clearly defined” standing operating procedure (SOP) for the type of approach.
It said: “The pilots had not developed a shared, unambiguous understanding of how the approach was to be flown.
“The operator’s SOPs at the time did not optimise the use of the helicopter’s automated systems.”
The report also pointed to the absence of a “well rehearsed plan for a diversion” in the context of poorer than expected weather conditions.
Twenty-six recommendations were made in the report, but the AAIB said many had already been implemented.
They included a call for the European Aviation Safety Agency (EASA) to introduce a requirement for pilots to receive initial and recurrent training in instrument scan techniques specific to the type of aircraft being operated.
It also proposed changes to cabin seating design layouts so that in an emergency each exit need only be used by a maximum of the two passengers directly next to it.
And it suggested the installation of cockpit and cabin image recorders, the introduction of a minimum size for all removable exits, as well as a common standard for emergency exit opening mechanisms.
Additionally, the AAIB said EASA should require existing helicopters used in offshore operations to have a means of deploying each liferaft above the waterline, whether the helicopter is floating upright or inverted.
It also concluded operators should be required to demonstrate all passengers and crew travelling offshore on their helicopters have undertaken underwater escape training at an approved training facility, to a minimum standard defined by the EASA.
In its conclusions, the AAIB stated the emergency breathing systems worked correctly, but were not used by the majority of passengers – either because they were unaware an air supply was available or because they were unable to locate the mouthpiece.
Those who escaped from the cabin used the windows as exits and a number of panes were displaced during the initial impact, with others removed by passengers.
They described this as being harder than they had experienced during training.
Both liferafts were successfully deployed by the co-pilot using deployment handles fitted to the underside of the helicopter fuselage.
But the report concluded he was only aware of the additional handles as a result of an informal conversation with a pilot who had instructed in the Norwegian sector.
Those used were not standard for UK helicopters and had been fitted when the helicopter was operated on the Norwegian register.
The report said the flight manual describing the additional liferaft deployment handles had not been updated to reflect the helicopter’s change of registration.