Sheriff Principal determines North Sea helicopter crash could not have been avoided

George Allison, Sarah Darnley, Gary McCrossan, and Duncan Munro were travelling to Shetland in the AS332 L2 Super Puma helicopter on 23 August 2013, when it crashed into the North Sea. The other passengers and both pilots survived, although one, Samuel Bull, sadly took his own life in 2017 as a result of post-traumatic stress disorder.

The inquiry was conducted by Sheriff Principal Derek Pyle, who also conducted a prior FAI into a Super Puma helicopter crash in the North Sea in 2014.

Below minimum operating speed

The helicopter was on its third flight of the day when the accident occurred, travelling to Shetland to refuel before flying back to Aberdeen. On board were 16 passengers as well as the pilot and co-pilot. Weather conditions were described as not good, with strong winds and highly reduced visibility.

Captain Martin Miglans, the commander, had over 10,000 hours of flying experience, while his co-pilot Alan Bell had 3,000. Mr Bell had only completed his training on the L2 six months before.

The flight path of the L2 deviated from the planned approach to Sumburgh Airport some 1,000 feet above mean sea level, falling below the minimum operating speed. The helicopter entered a low energy state, compromising the auto pilot’s control of the flight path, with it being too late for the commander to take remedial action once the minimum descent altitude had been reached.

Immediately before the L2 crashed into the sea Mr Bell armed the emergency flotation system, an action that was stated to have likely avoided further fatalities. Both pilots were injured in the crash, but they were able to escape the helicopter along with all of the passengers except Sarah Darnley and Duncan Munro.

George Allison died by drowning after escaping the helicopter but prior to reaching the surface. Gary McCrossan died after reaching the surface from cardiac enlargement and coronary artery disease triggered by the stress of the crash.

The Air Accident Investigation Bureau report into the crash concluded that the L2’s flight instruments were not monitored effectively during the latter stages of the approach. In his submissions, counsel for the Crown accepted that these failures may be explained by the difficulty, or perhaps impossibility, of pilots being able to continuously monitor flight instruments.

Contributory factors that were identified by the report included the operator’s Standard Operating Procedure for this type of approach not being clearly defined and not optimised for the use of the helicopter’s automated systems during a non-precision approach.

Pilots given discretion

In his determination, Sheriff Principal Pyle stated that the inquiry raised “fundamental issues about how air accidents should be investigated and the barriers which the Crown and Police Scotland face in carrying out their own investigation and over which they have no control”.

On the ultimate cause of the accident, he said: “At the end of the day we know that for whatever reason or reasons the commander failed to maintain the target approach speed of 80 knots. If he had done so, the helicopter would not have reached the critically low energy state from which recovery was impossible.”

He continued: “But it is difficult, indeed impossible, in my opinion, to come to any definite conclusions in a comprehensive way about what happened and why. We do not know, for example, whether Mr Bell was performing other duties during the critical phase when monitoring of the instruments might have allowed him to warn the commander about the drop in airspeed, such that his failure to notice the deceleration can be explained.”

Analysing the AAIB criticisms of the SOP, he said: “The fundamental point was that the SOP gave pilots a discretion as to how they would use the auto pilot during the approach. None of the experts said that this was wrong at the time of the accident. The fact that CHC removed the discretion after the accident is no more than an example of standard operating procedures being contained in a living breathing document which necessarily changes over time in the light of experience.”

Beyond Crown’s control

The Crown did not lodge the formal notice for the fatal accident inquiry until 21 November 2019, over six years after the accident, something for which it apologised. Sheriff Principal Pyle invited the Crown to explain what lessons they had learned from this and felt it important to comment on their response.

The Crown submitted that it was unable to properly conduct its criminal investigation into the accident until the AAIB had completed its own. This did not take place until March 2016. Further, the Crown was initially unable to identify an expert witness who would be able to issue a report on whether an ordinarily competent pilot would have followed the same course as the pilots. That report was issued in October 2018.

Sheriff Principal Pyle commented: “In the light of this explanation, I am satisfied that while the Crown apology was welcome there was no period over the last seven years during which the Crown failed to perform its duties diligently and expeditiously. On the contrary, the delay which did occur was beyond the Crown’s control.”

Dreadful accident 

The final declaration of Sheriff Principal Pyle was that no precautions could reasonably have been taken which would have avoided any deaths.

He concluded: “This was a dreadful accident with long term repercussions for the survivors and the families of the deceased which no determination by this court can properly describe. I do hope that it has at least assisted in an understanding of what occurred, the reasons for it and what has been done to ensure so far as practicable that such an accident does not occur again.”