ENGINEERS were warned about fuel reading "irregularities" on the type of helicopter which crashed into the Clutha pub by a pilot over two years before the tragedy.

Craig Trott, 49, who was a pilot and subsquently training captain with helicopter operators Bond (now Babcock) also revealed that he had found problem fuel readings with the type of helicopter that crashed, less than a week before the crash that claimed the lives of ten people on November 29, 2013.

Mr Trott said that he contacted David Price who was director of engineering at the aircraft's operators Bond (now Babcock) in June 2011 about "irregularities" over fuel readings, nearly two-and-a-half years before the Clutha crash.

He said when a Eurocopter Deutschland EC135 shut at a low fuel state and was left for a couple of hours, fuel appeared to to flow from the two supply tanks to the main tank "of its own accord". Mr Trott said that on one occasion, gauges showed that they were required to land in ten minutes, even though they had 40 minutes of fuel.

"At the time I was concerned that with nose down attitudes fuel was flowing from supply tanks into main tanks and the question in my mind was is the fuel in the main tank still accessible to me," he said.

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He told a fatal accident inquiry at Hampden that he had experienced that "unusual" situation before and "that's why I wanted to resurface these issues".

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In cross-examination by Donald Findlay QC, representing the partner of victim Robert Jenkins, Mr Trott said he was aware he not the only person experiencing fluctuations over fuel readings within the company with the aircraft.

"What I was noticing was there were these irregularities that I did not consider to be usual and I thought warranted further investigation," he said.

"Was I keeping an eye on the fuel? Yes. I was looking further at it.

"Were there further implications over the issues that I had raised? Yes there were."

In October 2015 a report on the Clutha crash from the Air Accident Investigations Branch revealed pilot error after both engines of the EC135 "flamed out".

In 2003, Airbus had been made aware of issues with fuel readings in its EC135 helicopters and this was suspected to have been caused by water rusting the the hydro mechanical unit (HMU), part of the fuel system.

The inquiry previously heard from AAIB senior inspector Marcus Cook that five separate low fuel warnings would have gone off in the doomed helicopter which smashed into the Clutha bar, and some of the warnings would have been made intermittently.

The 2015 Air Accident Investigations Branch investigation said that Clutha pilot David Traill, 51, one of the ten that died, did not follow emergency protocol and flew on despite low fuel warnings.

Mr Trott said that since raising the 2011 incident the reason for the phenomenon had never been explained to him.

Mr Price responded at the time in an email it would be looked into "and if required taken up with the Germans".

Two years later, in an email to Jim Remfry, head of maintenance at Bond he raised an issue that following a refuelling after a period of a couple of hours the readings of main tank levels had fallen from 310kg to 295kg when the helicopter had not moved.

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The fatal accident inquiry was later read a statement by Mr Trott to the AAIB in relation to the Cluth crash about fuel fluctuations he observed on November 23, six days before the Clutha crash.

"I was line training. Prior to start up, the fuel quantity was indicating 350 kgs. After the engines had been started, the fuel was indicating 345kgs. After lifting into the hover before take off the fuel quantity instantaneously dropped to 315kgs," he said.

"After take off... and accelerated to 220 knots, the fuel quantity went up to 325kgs."

He said he mentioned the issue to other pilots on handover and one of the line engineers was to be informed.

Mr Trott said that in hindsight the issue the issue could have been a sign of a problem with fuel probes in the main tank.

"All I was doing was reporting what I had seen [at the time]. I could not diagnose it much further than that," he said.

"We had a lot of instances of fuel probes giving slightly strange fuel readings.

"I was acutely aware of keeping an eye on the fuel guages for discrepancy."

In January 2, 2014, after the Clutha crash, an air ambulance showing "unusual" fuel readings ended up having fuel probes removed, cleaned, inspected and refitted.

The inquiry heard that the ill-fated police helicopter still had 73kg of fuel on board when it crashed.

Asked if he thought that would have been enough to get the helicopter back to its base at Glasgow City Heliport, Mr Trott said: "If the fuel is usable, yes."

Mr Traill; PC Tony Collins, 43; and PC Kirsty Nelis, 36, lost their lives in the crash along with seven customers who were in the bar on Stockwell Street.

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.

The inquiry, before Sheriff principal Craig Turnbull, continues.