A propeller injured two students working inside a hangar at the Pittsburgh Institute of Aeronautics, according to police.
A 20-year-old student was critically injured after he was struck in the head at the school's campus at the Youngstown Warren Regional Airport, Vienna Police Chief Bob Ludt told ABC News. He is still in the hospital.
(MORE: Yacht captain stopped trying to flee US after passenger was killed by propeller)A 28-year-old student has been treated and released from the hospital with injuries to his hand, Ludt said.
The propeller was not on a plane at the time of the incident but was on a motor on a stand, Ludt said. It is unclear how the propeller started up, but the fuel lines had been shut off.
(MORE: 6 animals electrocuted in 'freak accident' at South Africa's Kruger park)Several students were in the same workplace at the time of the accident but no one saw what happened other than the two students, Ludt said.
At the school, students are trained to assemble and disassemble engines on stands, but they do not start them inside the hangar, John Moliterno, executive director of the Western Reserve Port Authority, told the Tribune Chronicle.
(MORE: Freak tire accident kills college student at highway rest stop: 'It's heartbreaking for everybody')The names of the injured students were not released.