A LOW fuel warning was modified out of the Airbus EC135 class of helicopters around the time of the Clutha Vaults crash, it has been claimed.

The assertion was made by Peter Gray, representing Babcock, which took over the helicopter operator Bond Air Services after the tragedy on November 29, 2013.

The claim came as during cross-examination, Christian Bernhardt, a safety investigator with Airbus, accepted the onus was on the pilot to work out how the amount of time he had after the first engine flamed out for the second to go too.

Mr Gray had been questioning Mr Bernhardt, during the eleventh day of a fatal accident inquiry looking into whether lessons can be learnt over why the Eurocopter EC135 Police Scotland helicopter crashed through the Clutha roof.

Ten people were killed - including three helicopter crew - and 31 people were injured.

Mr Bernhardt agreed that with new generations of Airbus helicopters there is a positive requirement on pilots to ensure fuel pump switches are kept all at all times.

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

It found fuel transfer pumps were turned off and a controlled landing was not achieved for "unknown reasons".

Mr Bernhardt said he was not aware the newer Airbus H160 and new generation EC135s which have the Helionic software has a light that turned red on the main tank display at any time when fuel is not being transferred from the main tank to the supply tank.

And he said such an alteration could not have been employed on the EC135s that were used at the time of the Clutha tragedy.

"It is a completely different computer and software. It's just two different things," he said.

Mr Gray then asked if he was aware that 15 years ago on the old type EC135s that when the level of fuel in the supply tanks dropped to a certain level, the background colour of blue turned to another colour.

"On the EC135, you say?," said Mr Bernhardt.

"Yes," replied Mr Gray, who had earlier Mr said the older generation of EC135s, did have a digital reading of the amount of fuel in each of the supply and main fuel tanks.

Mr Bernhardt added: "I am not aware of that. I have never heard this before. You say we had it and removed it?"

Mr Gray said: "Exactly what I was going to come to. And that was modified out. There was a modification to the Avionics software...  You are not aware?"

"I am not aware of that," said Mr Bernhardt.

During further cross-examination by Donald Findlay QC, representing the family of victim Robert Jenkins, Mr Bernhardt indicated the pilot had "moments' to react after the first engine "flamed out" and it was down to him to work out how much time he had before the second went the same way.

Mr Findlay asked: "Why is there no information available to the pilot as to the period of time he will have before the second engine may flame out.

Mr Bernhardt said: "This information is the amount of fuel that is left in the supply tank and if he wants to know how much time he has he has to quickly...

"So it is up to the pilot to look at the guage and calculate the time he has left, is that right," asked Mr Findlay.

"If he wants to know he has to look at the guage," added Mr Bernhardt.

"If the first engine has flamed out, it's ten minutes it gives you to fly after a low fuel warning."

Mr Findlay added: "It might be thought he [the pilot] had enough to do when the engine flames out, without trying to work out how long he has before the second engine dies, or am I being unreasonable?"

"The pilot would, of course, expect that as he has low fuel warnings that after he lost the first engine, the second one will flame out in the next moments, and he has to land the aircraft," said Mr Bernhardt.

The latest developments come after the court was told helicopter manufacturers Airbus knew about issues with the EC135 model's fuel readings a decade before the Clutha crash.

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 Air Accident Investigation Branch 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, the investigation said.

One of the fuel tanks was empty, while a second contained 0.4 litres. A third contained 75 litres, but transfer pumps to take this fuel to the other two engine tanks were switched off.

And the AAIB recommended all police helicopters be equipped with black box flight recording equipment.

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.