A helicopter that ditched in the sea with the loss of four lives would not have crashed if the pilot had stabilised the speed on approach to the airport, an inquiry has heard.
Mark Prior, an expert pilot, said that if the pilot had stabilised the speed at 80 knots he would have been able to level off and would not have ended up losing control of the aircraft.
Two crew members and 12 passengers on the Super Puma L2 survived when it ditched on its approach to Sumburgh Airport in Shetland at 6.17pm on August 23, 2013.
But Sarah Darnley, 45, from Elgin, Moray; Gary McCrossan, 59, from Inverness; Duncan Munro, 46, from Bishop Auckland, County Durham, and George Allison, 57, from Winchester, Hampshire, died.
An AAIB report published in 2016 found that the pilots failed to properly monitor the flight instruments and failed to notice their speed was decreasing until it was too late to avoid the helicopter plunging into the sea.
Crown witness Mr Prior, a private aviation consultant who previously worked for the RAF for 40 years, prepared a report on the crash with three other pilot experts for the Fatal Accident Inquiry (FAI), which is being held virtually due to coronavirus measures.
Sheriff principal Derek Pyle, who is leading the inquiry, said: “What we know is, at some later point, the aircraft got down to the correct speed of 80 knots and that was more than two miles from Sumburgh Airport.
“In the event that the pilot who apparently said just after that point ‘right that’s 80 knots, that’ll do’, if the pilot had then stabilised the speed at 80 knots would the accident have occurred?”
Mr Prior replied: “In my opinion no, because if they had flown at 80 knots that would have allowed them to continue. There was still an issue due to the autopilot configuration, it would have been difficult to level, but, that point aside, they would have had enough energy to level off and perhaps commence a missed approach.
“Certainly they would not have been in a regime of flight where the manual handling of the aircraft became more difficult and in the end they lost control.”
The inquiry heard that later in the flight the air speed dropped from 70 knots to 35 knots over around 23 seconds and then crashed.
Mr Prior said he did not believe the crew scanned the instruments effectively during those 23 seconds because they had not noticed the drop in speed.
Asked what would have happened if this performance had been replicated in tests for an examination, he replied: “They would certainly have failed the test.”
Mr Prior said both the pilot flying (PF) and pilot non-flying (PNF) had responsibility for monitoring the air speed, though the PF had “more weight” in the role as the PNF had other tasks to carry out.
He told the inquiry that by the time the crew noticed the airspeed, when the helicopter was below 300ft, it was “too late” to recover the aircraft.
Martin Richardson QC, who is leading the inquiry for the Crown, asked which factors he considered particularly relevant to the cause of the accident.
Mr Prior said the accident followed a chain of events including the fact that if the crew had been aware of the weather before they set off they might have made different decisions.
He told the FAI: “Having commenced this approach, the major factors, I believe, are the fact that they did not achieve a stable approach, and because they did not achieve a stable approach that made them more prone to any errors in scanning, and so the secondary factor here is that the crew did not see the change in the air speed, they did not see the nose pitching up and they did not see the low power set.”
Mr Prior also told the inquiry that the lack of a stabilised approach meant they were not compliant with the operations manual.
Survivor Samuel Bull took his own life in London in 2017, which Sheriff Pyle said was “directly caused” by the crash.
The inquiry is being held virtually due to coronavirus measures.
A statement of agreed evidence read at the start of the inquiry confirmed that no mechanical fault was discovered with the helicopter, which was returning from the Borgsten Dolphin support vessel to Sumburgh Airport when it ditched.
The inquiry continues.