An off-duty pilot riding in the extra seat in the cockpit of a Horizon Air passenger jet in the US over the weekend tried to shut down the engines in midflight and had to be subdued by the crew, according to a pilot flying the plane. 

Authorities in Oregon identified the man as Joseph David Emerson, 44. He is now being held 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 was diverted to Portland, Oregon, where it was met by officers from the Port of Portland, who took Emerson into custody. 

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

The airline said the captain and co-pilot reacted quickly, and “engine power was not lost and the crew secured the aircraft without incident”. 

Alaska Airlines said in a statement that no weapons were involved. 

One of the pilots told air traffic control 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.net. “Other than that, we want law enforcement as soon as we get on the ground and parked.” 

The FBI office in Portland said it was investigating “and can assure the travelling public there is no continuing threat related to this incident”. 

The Federal Aviation Administration said it was helping law enforcement investigations, but declined further comment about the incident. 

FAA records indicate that Emerson has a valid licence to fly airline planes. 

There have been crashes that investigators believe were deliberately caused by pilots. Authorities said the co-pilot of a Germanwings jet that crashed in the French Alps in 2015 had practised putting the plane into a dive. 

In 2018, a Horizon Air ground agent stole an empty plane at Sea-Tac International Airport in Seattle and crashed into a small island in Puget Sound after being chased by military jets that scrambled to intercept the plane. The man told an air traffic controller that he “wasn’t really planning on landing” the aircraft, and described himself as “a broken guy”. 

The latest incident occurred on a 76-seat Horizon Air Embraer 175 that left Everett, Washington, on Sunday at 5.23pm local time and landed in Portland an hour later. Alaska Airlines did not immediately say how many passengers were on board. 

Alaska said passengers continued on to San Francisco on a later flight. 

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. 

-David Koenig and Claire Rush, Associated Press