Off-duty Alaska Airlines pilot charged with attempted murder after allegedly trying to shut down plane's engines during flight

An off-duty pilot has been arrested and charged with 83 counts of attempted murder after allegedly trying to shut down a plane's engines during a flight, causing the pilot to divert the aircraft.

Joe Emerson, who was sitting in the spare seat of the cockpit, was "subdued" by the two pilots flying the aircraft and arrested after the plane landed safely at around 6.30pm local time on Sunday evening.

Horizon Air flight 2059 from Everett to San Francisco was diverted to Portland, where the 44-year-old suspect was held by police.

Alaska Airlines, which owns Horizon, said in a statement on Monday that the flight was diverted due to a "credible security" threat linked to a person in the cockpit's flight deck jump seat.

"The jump seat occupant unsuccessfully attempted to disrupt the operation of the engines," the airline said.

"The Horizon captain and first officer quickly responded, engine power was not lost and the crew secured the aircraft without incident."

The flight crew followed "appropriate FAA procedures and guidance from air traffic control" in landing at Portland International Airport, the airline added.

Its statement continued: "The jump seat occupant is currently in custody and the event is being investigated by law enforcement authorities, which includes the FBI and the Port of Portland Police Department.

"All passengers on board were able to travel on a later flight."

After landing, Emerson was arrested by Port of Portland police and charged with 83 counts of attempted murder, 83 counts of reckless endangerment, and a count of endangering an aircraft, according to the Multnomah County Sheriff's Office, NBC reported.

No weapons were involved, the airline said.

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Audio of the plane's communications with air traffic control appears to reveal an attempt to turn off the plane's engines.

"As a heads-up. We've got the guy that tried to shut the engines down out of the cockpit. It doesn't sound like he's got any issue in the back right now. I think he's subdued," the pilot of the plane told air traffic control.

"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.

Typically, off-duty airline pilots sit in the jump seat of the flight deck behind the pilots to fly back to their home base if seats are available.