The mystery of Clutha helicopter pilot David Traill's actions during the final minutes before the fatal crash that claimed 10 lives dominated the Fatal Accident Inquiry last week.
Witnesses have told the inquiry, before Sheriff Principal Craig Turnbull, that the Air Accident Investigations Branch (AAIB) probe revealed that five fuel caution and fuel warning alerts had gone off, the first of them as the Police Scotland EC135 aircraft, registration G-SPAO, approached the Bothwell area.
Rather than returning straight to the Glasgow heliport, Captain Traill and his two police observers continued what has been described as 'routine' surveillance work in Bothwell, and also Uddingston and Bargeddie, before heading towards Glasgow that fateful night of 29 November 2013.
Captain Traill was described as a capable pilot by two police observers who had flown with him previously on several occasions. PC Niall McLaren, 45, a police observer for nearly 12 years to 2018, agreed that the pilot had been 'a stickler for procedure'.
PC Alan Graham, 43, said that he and PC McLaren had experienced a fuel warning on a previous flight with Captain Traill, but it had been when the aircraft had commenced landing. He added that the pilot had been content about safety because he had calculated his remaining fuel during the flight.
Rene Nater, 55, a test pilot for Airbus Deutschland with lengthy experience with the Dutch air force and also the Royal Air Force, told the inquiry that he had made two flights using a similar aircraft operated by the Lower Saxony police in Germany, attempting to re-create some of the issues experienced by the Police Scotland crew, as part of the manufacturer's post-crash investigation.
Asked about the circumstances faced by Captain Traill – with one engine failing, or 'flaming out', to be followed by the failure of the second engine just 32 seconds later – Mr Nater said that there would have been a brief two or three seconds of 'surprise' before he would expect a response.
He described in detail the actions taken by Captain Traill, who made several attempts at auto-rotation, a procedure that involves controlling a helicopter that has lost power in an emergency. With auto-rotation, the pilot attempts to glide the aircraft, using upward air in order to control speed. The pilot would then use a 'flaring' procedure to bring it down safely. This would be particularly difficult at night and in a city environment with so many buildings below. Captain Traill would have had just seconds to find a suitable space to land, all the while working at the controls.
Donald Findlay QC, acting for the partner of victim Robert Jenkins, asked Mr Nater: 'Somewhere between 900 and 1,000 feet, Alpha Oscar (G-SPAO) lost one engine. Are you telling us that from that point on that helicopter would have been doomed?'. The witness replied: 'If you had one engine failure you might have a chance. With two, you have no chance unless there is an open area in front of you'.
Within seconds, the aircraft had ploughed head-first into the roof of the busy Clutha bar, killing all three crew and seven customers below.
The inquiry had heard previously that Captain Traill switched off both pumps at an earlier stage of the flight, a procedure used at times to prevent over-heating. But Airbus had some years beforehand installed new pumps in the EC135 model, as they were found to be more reliable than a previously-used brand, according to evidence heard last week. The Test-Fuchs pumps did not require to be switched off. The court heard that operating manuals had not been updated to reflect the change.
Mr Nater was asked what he would have done when the first fuel warning had flashed before arrival over Uddingston. He replied that he would have started a dashboard-mounted stop-watch, as he would know he had to land within eight to 10 minutes. He would have checked the fuel and switched the pumps back on.
'Is that a practice of yours?' asked Mr Findlay.
'Yes,' replied the witness. 'A red light is always an immediate action and I don't know any pilot who would neglect it.'
Mr Nater said that pilots should have real-life training in auto-rotation in the EC135 in daylight, but that night-time training would be in simulation form only. Shelagh McCall QC, representing the partner of Captain Traill, put it to the witness that 'simulations are not the same as the real world, so doing it in the real world would be of benefit in an emergency?' Mr Nater replied: 'Absolutely.'
Earlier, the inquiry heard that Airbus had received 680 returns of fuel pump capacity sensors from operators who wanted them tested during a six-year period from November 2007 to October 2013.
Common complaints included faulty displays and spurious readings. Airbus fuel engineering expert, Holger Mendick, said that the number of sensors that were actually faulty was fewer, because operators either misunderstood readings, or had attributed faults to the fuel tank sensors, which were in fact traced to other equipment such as fuel bowsers.
Ms McCall asked the Airbus engineer: 'Operators appear to be having a great many issues with the sensors?'.
Mr Mendick replied: 'We had a lot of discussions with the operators'.
He acknowledged that there were problems, but added that sometimes the possible causes, such as contamination, disappeared when the sensors were removed from the fuel assembly, prompting speculation that the act of removal itself had cleared the problem.
Mr Mendick, responsible for compliance verification, acknowledged that the returns were 'a huge number'. He pointed out that with EC135 aircraft completing around 400,000 hours flying time worldwide, there would be a 'natural number' of failures. The overall failure rate of 9.4% he attributed to several reasons, one of them being 'strong indicator drift', defined as meaning inaccurate readings of more than 3kg of fuel.
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.
Maurice Smith will be attending and reporting on the Clutha FAI each week in SR