Bond Air Services, the operator at the centre of the probe into the EC135T2 crash in Glasgow, says it has identified "a number" of helicopters with a fuel indication problem, following its precautionary grounding of the type on 11 December.
No further details were available on the nature of the fault nor how many aircraft were affected by it, although Bond says tests centred on the "function and accuracy of the fuel indicator system" on its fleet of 22 EC135s.
It adds: "We did however identify a number of aircraft with the fuel indication anomaly. Having worked closely with the manufacturer, Eurocopter, to identify the immediate cause, we began a process of jointly testing the aircraft and are now sourcing and replacing the affected components."
It hopes to release the aircraft back to service by 15 December.
The National Police Air Service said on 11 December that in the light of the fault it was advising pilots of the EC135 on police operations to fly with a greater amount of fuel on board the helicopter.
Eurocopter was not immediately available to comment.