An off-duty pilot who was in a jump seat in the cockpit of an Alaska Airlines flight on Sunday has been charged with more than 80 counts of attempted murder after he tried to disrupt the engines, prompting the plane to divert to Portland, Ore., the authorities said.

Flight 2059, operated by Horizon Airlines, an Alaska Airlines regional subsidiary, left Everett, Wash., around 5:23 p.m. and was headed to San Francisco when it reported “a credible security threat related to an off-duty Alaska Airlines pilot who was traveling in the flight deck jump seat,” Alaska Airlines said in a statement on Monday.

“The jump seat occupant unsuccessfully attempted to disrupt the operation of the engines,” Alaska Airlines said in the statement, adding that the captain and first officer “quickly responded, engine power was not lost and the crew secured the aircraft without incident.”

A pilot told an air traffic controller that the man had tried to cut the plane’s engines, according to an audio recording posted on LiveATC.net, which shares live and archived recordings of air-traffic-control radio transmissions.

“We’ve got the guy that tried to shut the engines down out of the cockpit,” the pilot said, “and he doesn’t sound like he’s causing issues in the back right now. I think he is subdued.”

The pilot asked that law enforcement meet the plane upon landing.

The Port of Portland Police Department said in a statement that the flight crew “was able to detain the subject and the flight landed safely at Portland International Airport just before 6:30 p.m.”

The man was taken into custody without incident. The department identified him as Joseph D. Emerson.

According to the Multnomah County Sheriff’s Office, Mr. Emerson, 44, was booked into jail on Monday morning on more than 80 charges of attempted murder, a felony; more than 80 counts of reckless endangerment, a misdemeanor; and endangering an aircraft, a felony.

There were four crew members and 80 passengers on board the flight, a spokeswoman for Alaska Airlines said.

Michael Jernigan, who was a commercial airline captain for more than two decades before he retired from Alaska Airlines last year, said it was common practice for off-duty pilots to hitch a ride in the jump seat when shuttling to and from work.

He said he “never worried about it all.”

“Pilots behave themselves — they have a lot of money and time invested in their craft,” Mr. Jernigan said.

As a jump seat passenger, he said, he would stay quiet when the plane was below 10,000 feet. When it started cruising at higher altitudes, he said, he would often chat with the pilots, many of whom he got to know well over the years.

He said he could only speculate about what might have prompted an off-duty pilot to try to disrupt a flight. On most jets, he said, “you can just pull a switch and shut the motors down.” He called the episode “very, very strange.”

It was not immediately clear if Mr. Emerson had a lawyer. Messages left at a phone number listed under his name were not immediately returned on Monday, when sheriff’s office records indicated he was still in jail.

The Air Line Pilots Association, a union that represents commercial airline pilots, commended “the quick and professional response of the two pilots and entire flight crew in securing the flight deck and landing the aircraft safely.”

“The safety of the flying public and our crews is at the foundation of everything we do, and we are fully cooperating with authorities as they investigate this incident,” the association said in a statement.

The union said that airline pilots in North America work in “one of the most highly vetted and scrutinized careers, and for good reason.”

Pilots in the United States, the union said, are evaluated throughout their careers through training, medical exams and other programs, and are subjected to random flight checks by the Federal Aviation Administration.

The F.B.I. in Portland said in a statement that no injuries were reported on the flight and that the agency, which is investigating, “can assure the traveling public there is no continuing threat.”

A spokeswoman for the F.A.A. referred questions to the local authorities.

“All passengers on board were able to travel on a later flight,” Alaska Airlines said. “We are grateful for the professional handling of the situation by the Horizon flight crew and appreciate our guests’ calm and patience throughout this event.”