The widower of a police officer killed after a force helicopter crashed into the Clutha pub in Glasgow has said he is "deeply concerned and frustrated" by the outcome of an inquiry.

Mark Nelis's wife Kirsty was one of three helicopter crew members who died when the Police Scotland aircraft fell onto the pub roof on 29 November, 2013, killing seven customers.

Speaking out after a fatal accident inquiry (FAI) concluded captain Dave Traill's failure to ensure at least one of the fuel transfer pump switches was set to on caused the crash, he said the pilot was "trusted implicitly" by his wife.

The widow of her colleague Tony Collins, who also died in the crash, said he had felt the same way.

Criticising Sheriff Principal Craig Turnbull's ruling, Mr Nelis said: "Following the FAI determination, we find ourselves deeply concerned and frustrated with both Mr Turnbull's comments and the Air Accident Investigation Branch (AAIB) and its report(s).

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"The sheriff principal, in his determination, apportioned blame to Dave, which we found to be very disappointing.

"He has commented that the pilot 'took a chance' and made a 'conscious decision' to ignore the fuel warnings.

"We find these conclusions surprising given the surrounding evidence that the aircraft had numerous fuel reading issues prior to the incident and that a number of design changes have been made to this aircraft type since."

He added: "No-one knows, nor will ever know exactly what circumstances led Traill to make the decisions he did and the determination has not changed mine or my family's confidence and faith in him.

"We also have deep concerns with regards to the Aircraft Accidents Investigation Branch (AAIB), whom we believe should provide a fresh independent report in light of this determination as well as releasing all forms of their report as it developed."

Rescuers lift the police helicopter wreckage from the roof of the The Clutha (Getty)

He said a draft report was sent to interested parties before the final version being released late with "key points" changed without families being informed.

Lucy Collins believes her late husband would have wanted her to reiterate his confidence in Traill's ability.

"He trusted Dave implicitly as the hugely experienced and skilled pilot he was," she said.

Kirsty Nellis 'trusted' Traill, husband says (EPA)

"I feel this is important information that Tony would have wanted me to share.

"I felt that Tony's unwavering trust in Dave Traill was the most important and relevant information that we could contribute to the FAI."

Their comments follow Traill's fiancee Dr Lucy Thomas accusing the sheriff principal of opting to "sully" the pilot's "distinguished reputation" after the inquiry closed earlier this month.

Thomas, who broke six years of silence to make a public statement, said: "In my opinion, the Sheriff Principal's determination... insults the intelligence of those who know of the evidence presented at the inquiry and are aware of the content of the initial AAIB report.

"I find it distressing and incomprehensible that given months, not moments, to consider the facts, the Sheriff Principal has come to this conclusion," she added.

More than 100 people were at the pub when the helicopter crashed when heading back to base.

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The inquiry concluded the crash happened when the helicopter engines flamed out sequentially while airborne due to fuel starvation after the supply tank was depleted.

Mr Turnbull ruled the incident could have been prevented if the pilot had followed emergency procedures relating to low fuel warnings, and said Traill made a "conscious decision" to ignore five warnings he received, which led to "fatal consequences".

An AAIB spokesman said: "The AAIB stands by its final report and that, as the FAI has now concluded, the AAIB has no further comment to make."

The Crown Office declined to comment.

On the sixth anniversary of the accident, the a candlelit vigil was held at the Clutha Bar, formerly the Clutha pub.

It opened in 2015 after being closed for two years. Scotland's First Minister Nicola Sturgeon attended the opening of the new bar, saying in a speech: "It's a night of mixed emotions.

"On the one hand it is fantastic to see this great Glasgow institution, The Clutha pub, open its doors to customers again.

"But on the other hand we will never forget what happened here that night."

She also criticised the initial report, calling it "deeply disappointing" and said it appeared "to raise more questions than it answers".