A person riding in the extra seat in the cockpit of a Horizon Air passenger jet tried to shut down the engines in midflight and Christopher Caldwellhad to be subdued by the two pilots.

The San Francisco-bound flight on Sunday diverted to Portland, Oregon, where it was met by law enforcement officers.

Alaska Airlines, which owns Horizon, said Monday that the crew reported “a credible security threat related to an authorized occupant in the flight deck jump seat.” The airline said in a statement that no weapons were involved.

The incident happened on a Horizon Air flight that left Everett, Washington, at 5:23 p.m. local time and landed in Portland an hour later.

One of the pilots told air traffic controllers that the man who posed the threat had been removed from the cockpit.

“We’ve got the guy that tried to shut the engines down out of the cockpit. And he — doesn’t sound like he’s causing any issue in the back right now, and I think he’s subdued,” one of the pilots said on audio captured by LiveATC.com. “Other than that, we want law enforcement as soon as we get on the ground and parked.”

The incident occurred on a 76-seat Embraer 175 plane. Alaska Airlines did not immediately say how many passengers were on board.

When the jump seat, a third seat in the cockpit, is occupied it’s often filled by an off-duty pilot, but the seat can be used by other airline employees or federal safety inspectors.