The company that manages Ireland West Airport Knock has been fined a total of €10,000 for the illegal use of green diesel.
Connaught Airport Development Company Limited pleaded guilty to four counts of illegal use of green diesel in vehicles, including a de-icer, a snow plough, a small bus for transporting passengers, and a fuel tanker.
Tubbercurry District Court heard that airport management co-operated with officers employed by the Office of the Revenue Commissioners and accepted that green diesel was being used in 14 vehicles at the airport.
Evidence given outlined that officials claimed they were not aware the practice of using green diesel was illegal and that they had "always" used the fuel.
Solicitor Thomas Walsh, representing Connaught Airport Development Company Ltd, told the court there was no attempt to conceal the use of the fuel at the airport.
He added that management were of the belief that as the vehicles were not on public roads, the fuel was permitted to be used in airport vehicles.
Since the detection in November 2017, all use of green diesel has ceased at the airport.
Judge Kevin Kilrane said that as the airport had probably continued this practice for 30 years, the loss to Revenue would be "absolutely massive".
"There was no intention to defraud, it is a negligence matter more than intent to defraud," he said, adding that the airport was a vital link in the west.
The court was informed by prosecuting State solicitor for Donegal, Ciarán Liddy, that the maximum fine for each count was €5,000.
Judge Kilrane convicted Connaught Airport Development Company Ltd on all four counts, fining the company €2,500 in each matter.