PORTLAND, Oregon (AP) — An off-duty pilot riding in the extra seat in the cockpit of a Horizon Air passenger jet has been charged with over 80 counts of attempted murder after he allegedly tried to shut down the engines in mid-flight.

He had to be subdued by the crew, a pilot flying the plane told air traffic controllers.

Authorities in Oregon identified the man as Joseph David Emerson, 44. He was being held Monday on 83 counts each of attempted murder and reckless endangerment and one count of endangering an aircraft, according to the Multnomah County Sheriff’s Office.

The San Francisco-bound flight on Sunday diverted to Portland, Oregon, where Emerson was taken into custody by officers from the Port of Portland. He is to be arraigned Tuesday.

Seattle-based Alaska Airlines, which owns Horizon, a regional carrier, did not name Emerson, but said Monday that the threat was posed by one of its pilots who was off duty but authorised to occupy the cockpit jump seat.

The airline said in a statement that the captain and co-pilot “quickly responded, engine power was not lost and the crew secured the aircraft without incident.” Alaska said no weapons were involved.

One of the pilots told air traffic controllers that the man who posed the threat had been removed from the cockpit and was in handcuffs in the back of the plane.

“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.net. “Other than that, we want law enforcement as soon as we get on the ground and parked.”

Bailey Beck, who was on the flight, described to SFGate the confusion and stress experienced by passengers.

“It was really bizarre because there was no overheard commotion to alert the passengers. The man walked from the cockpit to the back of the plane by himself, where he was then handcuffed to a railing and didn’t make any disturbance from the rear,” Beck told the news outlet.

Sunday’s incident occurred on a Horizon Air Embraer 175 carrying 80 passengers, including children two or younger, and four crewmembers. The plane left Everett, Washington, at 5:23 pm local time and landed in Portland an hour later. Alaska said passengers continued on to San Francisco on a later flight.

The FBI office in Portland said it was investigating.

The Federal Aviation Administration, in an alert to airlines, said a jump seat passenger tried to disable the engines by deploying the engine fire-suppression system. The agency said it was helping law enforcement investigations, but declined further comment.

FAA records indicate Emerson has a valid license to fly airline planes. Property records show he owns a house in Pleasant Hill, California, about 30 miles (50 kilometres) east of San Francisco. The Associated Press tried but couldn’t reach family members.