The pilot of a police helicopter which crashed into a packed pub did not follow emergency procedures after a fuel warning in the cockpit, it has been reported.
The long-awaited Air Accidents Investigation Branch (AAIB) report into the Clutha tragedy in Glasgow on November 29, 2013, is being published today.
The pilot and nine others died when the helicopter fell from the sky and crashed through the roof of the busy bar.
The Scottish Sun newspaper said the report found that two fuel supply switches were off yet the helicopter continued to carry out three surveillance jobs over nearby Lanarkshire rather than land.
The pilot, David Traill, who was attached to Police Scotland's air support unit, was a highly experienced former RAF and training pilot with more than 5,000 flying hours in helicopters.
The report is said to state: "The investigation could not establish why a pilot with over 5,500 hours flying experience in military and civil helicopters did not complete the actions detailed in the Checklist Emergency and Malfunction Procedures for low fuel warnings."
It is understood the report will reveal that it remains unclear why the two fuel supply switches were in the off position, ultimately leading to both engines cutting out, and that it does not blame any individual for the crash.
Relatives were given an advance briefing on the AAIB's findings this week and said the report makes a compelling case for black box flight recorders to be fitted in all passenger-carrying aircraft.
More than 100 people were enjoying a night out at the pub when the police helicopter returning to its base on the banks of the River Clyde crashed through the roof.
In an interim report published last year, the AAIB said both engines on the aircraft failed but the cause was not outlined.
The interim report said the engines had ''flamed out'' before the helicopter crashed at 10.22pm, killing the pilot and two police constables on board as well as seven people in the pub. There was no flight data recorder on the aircraft.
Speaking after a family briefing on Wednesday, John McGarrigle, who lost his father John, said: "Flight data recorders should be installed in every passenger-carrying aircraft - simple as. If we had that, we would know a lot more. It's just question upon question upon question.
He added: "I'm furious. I came here very optimistic, very hopeful, knowing that the AAIB are very impartial but I just feel really let down by those guys because these are the people that we came here tonight to get answers off of and we never got any answers.''
Anne-Marie Kennedy, who was working behind the bar and was trapped in the wreckage, said: "It's shown me that they should have black boxes for defo, it's shown me the need for other regulation, but other than that nothing."
Ian O'Prey, whose son Mark died in the bar, said: "The pilot wasn't at fault, that's for certain.
"There were switches left on, or off, and the engine had fuel starvation, that's basically it."
The two others in the helicopter, police constables Tony Collins and Kirsty Nelis, were killed when it crashed into the building.
As well as Mr O'Prey and Mr McGarrigle, those inside the pub who were killed were Gary Arthur, Colin Gibson, Robert Jenkins, Samuel McGhee and Joe Cusker.
Jim Morris, partner at Irwin Mitchell solicitors and an expert in aviation law, said the investigation had been impeded by the lack of a black box flight recorder.