AN AIRBUS specialist put on hold a 'solution' to a flight safety issue over the Eurocopter EC135 on the day one of them crashed into the Clutha Vaults pub in Glasgow, an inquiry has heard.

Ten were killed when the EC135 police helicopter crashed through the roof of the bar in November, 2013.

Emails shown to the inquiry revealed that David Price, who was at the time director of engineering with helicopter operators Bond Air Services, alerted Eurocopter Deutschland, run by Airbus, and France-based engine manufacturers Turbomeca that there were issues with water contaminating the fuel supply of the EC135 in 2003, 10 years before the crash.

Mr Price, who appeared at day 15 of the fatal accident inquiry said that, despite his written concerns to Eurocopter in 2003 it was not until 2014, after the crash, that a 'final solution' air service bulletin was issued.

He had been concerned that the HMU (hydro mechanical unit) had been sucking water into the engine.

Ralf Nicolai, a 61-year-old sales promotion manager of Airbus, who Mr Price approached about the issue in 2003 had previously said that an investigation later found water contamination could also lead to fuel sensors giving an "over-reading" indicating the aircraft had more fuel than it did.

READ MORE: Clutha FAI: Disaster 'was an accident waiting to happen'

Bond issued a No Technical Objection document in November 14, 2013, 15 days before the Clutha tragedy, suggesting design changes including putting a vent into a drain pipe to eliminate the possibility of fluid being sucked by the HMU.

Mr Price said while Airbus had no objection, Bond had to seek further approval.

On November 29,  the day the Police Scotland helicopter G-SPAO crashed through the roof of the Clutha, Jorg Stuiver, who was described as a specialist working for Airbus, emailed Bond and said "the solution is not considered as the final solution... for serial production of fleet wide retrofit."

Mr Price said: "My interpretation on that was Airbus had not made a final decision on what the solution was and at this moment in time they were still evaulating what their final solution was going to be."

The email said that "a service evaluation should be carried out before the solution will be issued by SB (service bulletin)."

Six months later Airbus issued a service bulletin recommending the retrofitting of vent hoses on the fuel pump drain lines.

The inquiry is trying to find answers as to why Police Scotland helicopter G-SPAO crashed through the roof of the Clutha.

In October 2015 a report from the Air Accident Investigations Branch revealed pilot error.

It found David Traill, 51, one of the ten that died, did not follow emergency protocol and flew on despite low fuel warnings.

The inquiry had previously heard a police inspector who worked with the crew on board the doomed Clutha helicopter told about a history of problems with the aircraft's fuel indictators. Inspector Nicholas Whyte also speculated that the accident may have happened as the fuel warning lights did not come on in the cockpit saying that police air observers Kirsty Nelis and Tony Collins would never ignore red warning lights.

The inquiry was also previously told an air ambulance pilot was forced to land after receiving a false low fuel warning in Manchester in December, 2013, the month after the Clutha tragedy, after which Airbus launched a "worldwide fleet check" of 1000 EC135s.

Mr Price, 56, who is now the head of maintenance and engineering with the Babcock Aviation Group, told the inquiry of his "great frustration" over how the helicopter manufacturer had dealt with the water problem.

He said: "In 2003, one of our primary considerations of risk was the water getting directly into the engine fuel system."

He said an investigation found it was the result of a modification which meant that water was going directly into the fuel system.

He said in a 2003 email to Mr Nicolai: "The HMU (hydro mechanical unit) has been sucking water into the engine during the start cycle and some is returning to the tank and as the engine accelerates past 5%, some water passes into the engine fuel system (cleaning the filter assembly).

Mr Nicolai responded to his email saying: "We are on the case now, doing our homework as usual."

Two years later, Mr Price emailed Mr Nicolai and others saying: "I am somewhat concerned that from my perspective what was and still is a flight safety issue has not been prioritised in the manner I feel it should have....

"The HMUs that were the subject of the original report failed last July [during a check]...this in effect was a double HMU failure, a situation that does not make myself or anybody else feel very happy, especially as the potential warning signs had been raised some considerable time ago and and on a number of occasions since."

He added that there was a "worldwide issue here to be considered which is why I raise the issue again."

Mr Nicolai told Mr Price in an email that he had been informed a follow up by the design department had been held up "due to other priorities".

He added: "They will pick it up now again and process asap."

Mr Price, a former RAF corporal, said a final solution emerged in 2014 through the service bulletin, not before Bond had introduced an interim solution.

Mr Price admitted becoming frustrated by an email from Kelly Brookes of Eurocopter which said that a modification considered did not seem to make any difference.

"There was a feeling of great frustration on a number of occasions over ten years... and it was fair to say this was a very frustrating response," said Mr Price who felt the company were passing the buck back to Bond.

"What is basically conveyed here is, 'you use your design department, rather than us using our design department to come up with a solution'.

"Considering the correspondence that had gone on historically, it was clear that they had taken action to resolve this and felt that even after all this time, now they are asking us to invest in producing a modification and trial it to resolve the issue."

Pilot David Traill, 51; PC Tony Collins, 43; and PC Kirsty Nelis, 36, died along with seven customers who were in the bar, Gary Arthur, 48; Joe Cusker, 59; Colin Gibson, 33; Robert Jenkins, 61; John McGarrigle, 58; Samuel McGhee, 56; and Mark O'Prey, 44.

The inquiry before Principal Sheriff Craig Turnbull continues.