QUESTIONS have been raised over the actions of a pilot in the minutes before the Clutha helicopter crash as the Crown Office vowed to hold a Fatal Accident Inquiry into the disaster “as soon as possible”.

It comes after the final report by the Air Accidents Investigation Branch (AAIB) revealed that pilot Captain David Traill had ignored a series of low fuel warnings and continued flying for around 20 minutes before the crash.

Switches which control the flow of fuel to the engines were also turned off in the police helicopter, when they should have been on.

Ian O'Prey, whose son Mark died in the disaster, said the report offered no answers for those who had lost loved ones.

"I went in there expecting nothing and nothing is what I got," he said. "They just said the switches were off, but they don't know why they were off and they would never know why they were off.

"They didn't apportion any blame at all and I don't want to go down that road because the pilot's family have to listen to all the nonsense that is being said.

"I don't have any proof, but I think it was a machine malfunction."

Criminal prosecutions in relation to the tragedy have not been ruled out although investigators found no technical fault with the aircraft and its maintenance records were found to be up to date and correct.

Police chiefs said an “extensive major investigation” is underway and the report’s findings will now be used to decide whether charges should be brought.

Once the police case is closed, the Crown Office can proceed with an FAI.

Police constables Kirsty Nelis and Tony Collins, who were travelling in the Eurocopter EC135 with Captain Traill, were among those killed when it plunged onto the roof of the Clutha Vaults pub in Glasgow on November 29 2013.

John McGarrigle, Mark O'Prey, Gary Arthur, Colin Gibson, Robert Jenkins, and Samuel McGhee, who were inside the pub, were killed when the roof caved in. Joe Cusker, who was also at the venue, died from his injuries in hospital 13 days later.

A spokesman for the Crown Office said: "The report raises a number of questions for which the families of the victims deserve answers.

"The Crown will now conduct further investigations into some of the complex issues raised by the AAIB report. We will endeavour to do this as quickly as possible but these matters are challenging and the necessary expertise is restricted to a small number of specialists. We will continue to keep the families advised of progress with the investigation.

"As this tragedy involves deaths in the course of employment a Fatal Accident Inquiry is mandatory. This will be held as soon as is possible."

Andrew Henderson, a partner at Thompson Solicitors, which is representing 40 victims of the Clutha disaster, said an FAI was "the most robust way of getting to the truth".

He added: "At the end of the day we cannot have a situation where aircraft crash into urban areas causing loss of life and not know definitively why that happened. Only by knowing the full cause can we prevent something similar happening.”

Investigators have demanded that black box flight recorders be fitted to all police helicopters.

The devices should be able to store audio and images from inside the cockpit for at least the final two hours of a flight.

Data from black box recorders has been vital in unravelling the circumstances of recent airline catastrophes, such as the deliberate crashing of a Germanwings passenger plane into the Alps in March.