Clutha crash: What we know about the final flight

The helicopter's first task was responding to a report of a person who had been struck by a train in Oatlands, on the south side of the city.

The aircraft, operated by Bond Air Services, had been in service since August 2008 and responded to a variety of calls across the country, ranging from firearms incidents and vehicle pursuits to locating farm animals in heavy snow.

Capt Traill, a former RAF pilot, was joined by PC Tony Collins and PC Kirsty Nelis on a clear, moonless night.

The crew had two means of communication, both of which were recorded.

It was the responsibility of the pilot to liaise with Air Traffic Control and, separately, the Police Scotland Airwave system was used for operational purposes.

The history of the flight was traced using radar returns. Crucially, the helicopter was not fitted with a black box flight recorder which could have given a vital insight into what happened on board.

A key reference point for the inquiry was the 176-page Air Accidents Investigation Branch (AAIB) report into the disaster, which was published in October 2015.

It reported that at 21:22 the aircraft set off for Dalkeith, Midlothian - 42 nautical miles away - for a surveillance task which lasted just three minutes.

By 21:45 the helicopter was heading back to Glasgow but before it reached Bothwell, South Lanarkshire, at 22:06, the pilot was presented with the first of five low fuel warnings.

Each time a fuel warning illuminated on the helicopter's control panel it was accompanied by an "audio gong" which would be heard by anyone in the helicopter.

The warning must be acknowledged and suppressed by pressing a button.

The AAIB report was unable to determine precisely when the warnings activated but it noted each time Capt Traill acknowledged the gong.

Marcus Cook, senior inspector of air accidents at the AAIB, told the FAI that police helicopter pilots have an "acute fuel awareness" due to the non-routine nature of their work.

Capt Traill was instructed on the helicopter's fuel system during his initial conversion training in 2008 and had completed 646 flying hours in the EC135.

A key part of the training was the instruction to land within ten minutes of being presented with a fuel warning. But the inquiry heard the pilot was presented with a further four fuel warnings during the fateful flight.

Despite this three further surveillance sweeps in Bothwell and Uddingston, both South Lanarkshire and Bargeddie, North Lanarkshire, were carried out.

The FAI heard Capt Traill, who had thousands of hours of flying time, was described as a "safe pair of hands" and a "stickler" for the rules.

This begs the question why would a vastly experienced pilot agree to three further tasks if he had been confronted with an emergency fuel situation?

Evidence was also led that the two fuel pumps - which supplied fuel to the twin engines - were switched off, together or independently, at some point or points between Dalkieth and Bothwell.

This action may have been taken as they were showing as "dry" due to the tilt of the aircraft leading to fuel sloshing or over spilling. The pumps may also have been overheating, which can cause an explosion.

A video simulation of the helicopter's last flight, produced by manufacturers Airbus, noted: "There is no explanation why the pumps both came to be in the off position."

PC Collins and PC Nelis, who was sitting in the front seat, were also trained to intervene if they were in any way concerned about a pilot's actions.

During his evidence Insp Nicholas Whyte, of Police Scotland's Air Support Unit, was asked to assess what went on in the cockpit.

He replied: "It does not make sense that that flight would continue for the length of time that it did given the evidence we have over the red warnings.

"It does not make sense that those individuals that I knew continued with that flight. It does not make sense."

Insp Whyte was also asked why the crew did not raise the alarm if, hypothetically, Capt Traill was dismissive of their concerns.

He told the inquiry: "The only theory that I can present is that they actually were not presented with the warnings that we saw."

This implies no fuel warning lights were illuminated on the control panel and the gongs the pilot responded to occurred in isolation.

Despite this hypothesis the inquiry found no evidence the aircraft's Cautionary Advisory Display failed prior to the accident.

At 22:19 Capt Traill informed Air Traffic Control that the helicopter was returning to Glasgow City Heliport.

When he signed off the pilot had given no indication of any fault or any concern.

And at no point during the flight did he issue PAN or a Mayday call.

Two minutes later, at 22:21, the helicopter's right engine flamed out while it was travelling at a speed of 100 knots.

Investigators established the left engine flamed out 32 seconds later, while the aircraft was between 500 and 600ft from the ground.

Mr Cook said: "From the point the second engine flames out he [the pilot] had less than ten seconds."

On the ground witness Andrew Bergen saw the helicopter flying over the Clyde and told the court: "It made what I can only describe as a spluttering noise".

The solicitor said the helicopter's tail dipped and pointed toward the ground.

He added: "Simultaneously the lights went out and it seemed to me that the rotor stopped spinning. It was still turning but not under power."

Taxi driver Tariq Malik, was in the car park of the Grand Mosque on Ballater Street, on the opposite side of the river. He recalled: "All I could hear was a swooshing sound as it fell through the sky."

Ernest Docherty heard the helicopter behind him before he saw it. He told the court: "It was like an old car trying to start but a thousand times louder."

More than 100 people were in The Clutha Bar when the helicopter crashed into the roof and customers were enjoying a live set by the Ska band, Esperanza.

The inquiry did not hear any evidence from the survivors or the emergency service personnel and passers by who responded to the tragedy. The aircraft was later found to have 76kg of fuel - 9kg less than the recommended minimum - in the main tank but both supply tanks were empty.

As well as Capt Traill, PC Collins and PC Kirsty Nelis seven customers who were in the bar on Stockwell Street lost their lives . They were Gary Arthur, 48; Joe Cusker, 59; Colin Gibson, 33; Robert Jenkins, 61; John McGarrigle, 58; Samuel McGhee, 56; and Mark O'Prey, 44.

A further 31 people were injured.

The dead were remembered with a minutes' silence when the inquiry started in a temporary court at Hampden Park on 8 April. On the third day the court later heard a joint minute of agreement which revealed when and how each victim died.

The weeks that followed featured hours of technical evidence which at times was difficult to follow. The court heard the crash was the first reported instance of "fuel starvation" since the model was launched in 1996.

The inquiry was also told that the initial AAIB investigation was hampered by a lack of evidence, which expert witness Peter Wivell admitted was "frustrating for everyone".

Concerns were raised about the level of maintenance carried out on helicopters in Glasgow and on the day before the crash an engineer described the issue as "an accident waiting to happen".

The FAI also heard testimony about faulty fuel warnings and a fuel tank water contamination concern.

One criticism was that victims did not feature enough during the proceedings. Indeed the only insight into the human impact came on the opening day when statements were read out on behalf of six of the ten families.

The court heard Colin Gibson was celebrating a friend's birthday and had never been in the bar before, while John McGarrigle was a Clutha regular who always sat in the same seat. Tributes were also paid to Samuel McGhee, Gary Arthur and Mark O'Prey.

But perhaps the most poignant was the statement read out by Donald Findlay QC, representing Robert Jenkins' partner Mary Kavanagh. She last saw the 61-year-old as he walked to the bar to buy her a cranberry juice.

Mr Findlay said: "All Mary wants to know is why she went into the bar with the man she was going to spend the rest of her life with and came out alone."