Alaska Airlines Flight 2059, operated by Alaska Air Group’s regional subsidiary Horizon Air, departed Everett, Washington, on Sunday bound for San Francisco but was re-routed to Portland after reporting a security threat, the airline said.

The fight was carrying 80 passengers, including children 2 or younger, and four crewmembers. Alaska Airlines said all passengers on board travelled on a later flight.

The Federal Aviation Administration (FAA) told US airlines in a notice seen by Reuters that the off-duty pilot, flying as a “validated jump seat passenger”, sought to disable the engines of the twin-jet Embraer 175 by attempting to activate the engine fire-suppression system while the plane was at cruise altitude.

“The crew was able to subdue the suspect and was removed from the flight deck,” the FAA notice said. The engines were never disabled, Alaska said.

Sunday’s fight was carrying 80 passengers, including children 2 or younger, and four crewmembers.

Radio chatter from the flight deck moments later was captured on audio posted by LiveATC.net, an online service that streams communications between air traffic control and commercial jets.

“I’ll just give you a heads-up. We’ve got the guy that tried to shut the engines down out of the cockpit,” the Horizon pilot told air traffic control, according to the audio. “It doesn’t sound like he’s causing any issue at the back. I think he’s subdued. … We want law enforcement as soon as we get on the ground and parked.”

Port of Portland police officers met the flight and took the suspect into custody without incident.

An FAA pilot database showed Emerson listed as a certified pilot who received a medical clearance last month. Aviators are expected to self-report any mental health conditions, two US pilots told Reuters.

The Air Line Pilots Association (ALPA), the world’s largest pilots union, which represents aviators at Alaska, said in a statement that the airline “profession in North America is one of the most highly vetted and scrutinised careers”.

Adam Silverthorne, president of California-based NRI Flying Club, said the incident was incongruous with the kindhearted, methodical family man he knew Emerson as several years ago when Emerson was a club member and flight instructor. A club newsletter mentioned Emerson was at NRI in 2016.

“To say that it was out of character would be a huge understatement,” Silverthorne said by phone. “It’s bonkers.”

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

The FAA told airlines in a separate notice on Monday the incident “is not connected in any way, shape or form to current world events” but said it is “always good practice to maintain vigilance”.

It is standard practice for off-duty pilots to sit in jump seats for flights home or en route a future flight assignment.

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 practiced putting the plane into a dive.

In 2018, a Horizon Air ground agent stole an empty plane at Seattle’s Sea-Tac International Airport and crashed into a small island in Puget Sound after being chased by military jets that scrambled to intercept the aircraft.

The man told an air traffic controller that he “wasn’t really planning on landing” and described himself as “a broken guy”.

Additional reporting by Associated Press