Pilot error responsible for fatal Sumburgh crash, AAIB report reveals
Two and a half years since the crashing of the Super Puma helicopter in the UK North Sea, in which four workers died, the Air Accidents Investigation Branch has found that the pilots’ inattention to the flight instruments was the cause.
At 1717 hrs UTC on August 23 2013, an AS332 L2 Super Puma helicopter with sixteen passengers and two crew on board crashed in the sea during the approach to land at Sumburgh Airport. Four of the passengers did not survive.
The helicopter had been on its way from the Borgsten Dolphin semi-submersible drilling rig in the North Sea, to route to Sumburgh Airport for a refuelling stop. It then planned to continue to Aberdeen Airport.
According to the findings published on Tuesday by AAIB, upon being cleared to land to Sumburgh airport, the airspeed of the helicopter started to drop steadily unobserved by either the pilot or co-pilot, allowing the helicopter to enter a critically low energy state, from which recovery was not possible.
Right before the accident the co-pilot drew the commander’s attention to the airspeed, which was about 35 kt and the helicopter was descending at 1,000 fpm. The commander acknowledged the co-pilot and began to increase the collective pitch, however it was too late, and rate of descent increased to 1,800 fpm and he was not able to prevent the helicopter from impacting the water.
Following impact with the water, the helicopter rolled upside down and rapidly filled with water but remained afloat, inverted on the surface, supported by the floats which had inflated automatically. Twelve passengers and two crew members escaped from the helicopter and survived the accident. There were four fatalities: two passengers did not escape from the upturned fuselage, one passenger was found by the coastguard helicopter, lifeless, floating on the surface and one passenger, who had successfully escaped, subsequently died in one of the liferafts.
According to the report, after the accident, the co-pilot stated that he did not consider that 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 during an instrument approach. Additionally, he considered that he had not received guidance as to when, as PNF, he should look outside during an approach to acquire the visual references required for landing.
When interviewed by the AAIB, neither pilot was able to explain exactly what had happened during the latter stages of the approach to Sumburgh, nor why it had happened. The commander stated he had no recollection of events between the time the helicopter passed 4 DME and just before impact, when he caught sight of the sea surface and attempted a recovery. He stated that it had been his intention to carry out up to two approaches at Sumburgh and then decide on where to divert.
AAIB said that the co-pilot provided information to the investigation on the day following the accident and during subsequent interviews. He had a good recollection of most events, but did not have a complete picture of what had occurred during the latter stages of the approach. He stated, at interview, that he had been relying on the commander’s greater experience and had therefore not challenged his comments during the approach briefing.
The co-pilot stated that he had accepted the helicopter’s deviation below the published vertical profile during the latter stages of the approach because this was allowed and he had seen other approaches flown in this way. He commented that during the final approach he had noticed the commander looking up at some stage, perhaps seeking external visual reference, AAIB said.
No warning to the passengers
The report further reveals that during the final stages of the approach, the helicopter was in cloud and those passengers looking out of the windows were unable to see the land or the sea. As the helicopter emerged beneath the cloud, the commander attempted to climb the helicopter and the co-pilot armed the helicopter’s flotation equipment.
The rolling and pitching motion of the helicopter, combined with the descent towards the sea, caused alarm amongst the passengers, with some adopting the brace position. The passengers received no warning of the impact from the flight crew.
The helicopter had rolled to the right and was rolling back to the left when it struck the sea. On impact, the helicopter immediately rolled over to the left and the flight deck and passenger cabin filled with water. The water immersion switch activated on contact with the water and the floats inflated. Neither pilot had time to take a breath before they found themselves upside down and with no visual references. The co-pilot, who had been leaning forward at impact, received a head injury. The commander suffered a serious back injury as a result of the impact. Four passengers who died were Duncan Munro, 46, from Bishop Auckland, Sarah Darnley, 45, from Elgin, Gary McCrossan, 59, from Inverness, and George Allison, 57, from Winchester.
Cause of the accident
In its report, under the Causal Factor section, AAIB says:
- 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.