THE discovery of a series of fuel tank issues has raised new concerns about the safety of aircraft of the same model as the police helicopter that crashed into a Glasgow pub killing 10 people.
It comes as an Air Accidents Investigation Branch (AAIB) report into the Clutha Bar disaster found both engines of the Eurocopter EC 135 failed, although the cause was not clear.
The report said while 76kg (168lb) of fuel was left in the main fuel tank there had been a low-fuel warning. According to the manufacturer's flight manual this would indicate a pilot would need to land the helicopter within 10 minutes.
The Police Scotland helicopter came down on November 29 last year, killing seven people in the pub and its three crew.
Eurocopter has been making fuel-tank system checks of the worldwide EC 135 fleet and found issues in nearly 20 helicopters out of 467 tested. Some 44% have been tested.
Since mid-January, 16 fuel tank sensors needed to be cleaned and made "functional". Three had failed and had to be replaced.
Problems continued to be found after air services company Bond Aviation grounded its fleet of 38 EC 135s on December 11 after the North West Air Ambulance, one of its 22 aircraft leased in Britain, was found to have a fuel indicator problem.
The following day Bond confirmed aircraft having "no fault" would return to service and that the grounding was a "precautionary measure".
Eurocopter said at the time that the decision taken by Bond did not apply to the rest of the Eurocopter fleet in the UK - a total of 57 aircraft.
Four days later, Eurocopter issued a safety alert to operators of EC 135 helicopters as further fuel indicator defects were found.
Crews were warned by Eurocopter that in the worst case a red "low fuel" warning would appear without any amber "fuel caution" warning before.
It was not yet clear whether these issues are linked to the Clutha bar crash, some experts say.
The Police Scotland helicopter was minutes away from home when it dropped on to the roof of the pub.
The latest AAIB report into the Clutha crash said the flight's warning unit recorded intermittent Low Fuel 1 warnings for the left fuel tank supply, then a permanent Low Fuel 2 warning for the right fuel supply tank. This was followed by a further Low Fuel 1 warning before it became permanent for the remainder of the flight.
A spokesman for the British Airline Pilots Association said: "We now know that the engines were not running at the time of the crash and it appears this was to do with the fuel system. However, pilots, like the AAIB, will not be satisfied until this is explored further and the exact reason for that failure is identified."
Solicitors Irwin Mitchell's aviation law team, representing victims, has written to MPs and MSPs calling for a public inquiry into helicopter safety and for all commercial passenger helicopters to be fitted with flight data recording (FDR) equipment.
Jim Morris, a former RAF pilot and partner with the team, said: When a low fuel warning occurs on a helicopter of this kind, it indicates there is approximately 60kg fuel remaining, which requires the pilot to land within 10 minutes.
"As there is no indication of problems with the engines, gearbox or flying controls, it appears that a serviceable aircraft crashed due to some form of fuel starvation, despite having 76kg of fuel in its tanks. - this is something that should have never happened."
Hannah Bennett, a lawyer from Thompsons Solicitors' specialist Clutha legal team who represent 50 victims of the tragedy added: "It would appear there was a problem with the supply of fuel to the aircraft's engines, but questions still remain as to why both engines failed while there was still a significant amount of fuel on board and why no emergency radio transmissions were sent by the pilot."
A spokesman for Airbus Helicopters, the rebranded name for Eurocopter, said it "does not speculate on potential causes of any accident and continues to actively support the ongoing investigations of the AAIB".