The U.S. Department of Transportation’s Federal Aviation Administration (FAA) proposes a $617,100 civil penalty against Oklahoma-based Interstate Helicopters for allegedly conducting illegal charter flights.

The FAA alleges that between September 2016 and April 2017, Interstate Helicopters conducted approximately 24 paid passenger-carrying flights in jet airplanes when it was only authorized to conduct flights in helicopters.

The FAA further alleges the company used unqualified pilots who did not complete required training, testing, and competency checks for the 24 flights.

Interstate Helicopters has 30 days to respond to the FAA after receiving the letter.