A taxiing airplane’s wing struck a United Airlines tug driving at Chicago O’Hare International Airport, flipping the vehicle over and pinning the driver underneath it, police said.

“The victim and driver of the tug, a 64-year-old male, was transported to Lutheran General Hospital in critical condition where he has been stabilized,” Chicago Police said in a statement. “The victim sustained head and lower body injuries.”

United identified the man as an employee, adding that the airline was “ensuring he receives any necessary support and care.”

The tug had been attempting to cross a runway at about 7 p.m. Saturday when it was struck, according to police and the Chicago Department of Aviation. Tugs are ground vehicles that help move aircraft, including helping them park, while they’re on the ground.

The plane that struck the tug had flown in from Kalamazoo, Michigan, as American Eagle flight 6181, which was operated by Air Wisconsin, according to American Airlines.

“Nothing is more important than the safety of our customers and team members, and we are reviewing this incident,” American said in a statement.

None of the crew members or passengers on the plane were injured, the airline said, adding, “Customers deplaned safely and were transported to the terminal.”

Air Wisconsin is an air carrier affiliated with American Eagle, which is American Airlines’ regional carrier network.