Two air accident investigators expressed their bemusement and frustration as they recounted their probe into the Clutha helicopter crash, as they attempted to pinpoint what actually happened during the flight that ended in tragedy.
The 2015 report, compiled by an experienced team from the Air Accident Investigation Bureau (AAIB), concluded that while the EC-135 Police Scotland aircraft contained 76kg of fuel in its main tank, the supply tanks to its two engines were dry because the pumps which fed them had remained switched off.
The conclusion at the time was that, as the only person to have had control of the pump switch, Captain David Traill was responsible for the failure, the conclusion drawn being that the disaster resulted from pilot error.
Questions have been raised during the current Fatal Accident Inquiry (FAI), however, with suggestions that in certain circumstances the aircraft might have shown inaccurate readings of the remaining fuel. The AAIB report painted a detailed picture of the ill-fated flight, from the moment the aircraft took off from its base at Glasgow Heliport near the Clyde at 8.44pm on 29 November 2013. It depicted how the craft, registration G-SPAO, undertook search operations at Oatlands, Glasgow, for 33 minutes before heading directly east to Dalkeith, Midlothian, for what has been described as 'routine surveillance'.
It was on the return westwards that the AAIB calculated that the first of five fuel warnings would have been given to the pilot and crew, somewhere between Shotts and Bothwell, Lanarkshire, where Captain Traill and his police observer colleagues decided to undertake another surveillance task. They moved from Bothwell to Uddingston and then Bargeddie before heading back to the heliport – all the while receiving those fuel warnings.
This account of the entire journey, and what was possibly happening in the cockpit as well as the fuel tanks, have been based on estimates using radar signals recorded at various points of the journey, as well as data held within some components' memory chips recovered after the crash.
'The problem with this investigation was a lack of evidence that would have given a definitive answer, which is frustrating for everyone and not a good way of pursuing safety,' Peter Wivell, 48, a senior inspector specialising in engineering and data with 16 years' experience working for the AAIB, told advocate depute Sean Smith.
Mr Wivell added that more advanced flight recording equipment would have helped find the root cause of the accident, for example by showing a visual image of what the pilot and crew might have seen on the cockpit display at any stage during the entire flight. 'It could have captured an image of the display panel. If we had an image we would have been in a better position. It would have definitively been possible to say when the warnings appeared, and how long for,' he added.
The calculations estimate that the fuel pumps had been switched off by Captain Traill whilst heading westwards on return from Dalkeith. Witnesses have pointed out that this act in itself might not be unusual; such pumps can be temporarily switched off to prevent overheating. Similarly, fuel readings can vary according to the pitch or attitude of an aircraft as it travels; a helicopter may proceed slightly 'nose down' as it moves in a straight line. A 3D video of a simulated flight which was presented to the inquiry last week demonstrated that fuel levels in the main and supply tanks can change if, for example, the helicopter makes banking or turning manoevres during normal flight activities.
Mr Robert Vickery, 56, another senior inspector with AAIB with 30 years' experience as a Royal Navy aircraft engineer and investigator, told the inquiry that he examined the fuel tanks, fuel supply and sensors once the helicopter had been moved to a secure space after it was taken from the crash site. He had also inspected the aircraft during its removal, as colleagues sought to secure the craft for transportation.
Shelagh McCall, QC, acting for the partner of Captain Traill, Dr Lucy Thomas, asserted that the operators of the aircraft had expressed concerns about erroneous fuel calculations on EC-125 helicopters.
'It appears that they had reports (of erroneous calculations) since 2003?' asked Ms McCall.
'Yes, that appears to be correct,' responded Mr Vickery.
'Did you understand that as far as the operators were concerned, on some of those occasions no fuel was found with the sensor, or any contamination of the fuel?'
'Yes, and hence the frustration,' replied the witness.
A manufacturer's safety notice was issued by Airbus Helicopters on 16 December, just 17 days after the Clutha crash, recording the operator's concern that sensors may be over-estimating fuel.
The victims of the crash included bar customers Gary Arthur, 48; Joe Cusker, 59; Colin Gibson, 33; Robert Jenkins, 61; John McGarrigle, 57; Samuel McGhee, 56; and Mark O’Prey, 44. The helicopter crew included pilot David Traill, 51, and police officers PC Tony Collins, 43, and PC Kirsty Nelis, 36. The inquiry continues, with witnesses from Police Scotland and air traffic control expected to give evidence this week.
Maurice Smith will be attending and reporting on the Clutha FAI each week in SR