PORTLAND, Ore. (AP) — What authorities describe as an off-duty pilot's attempt to shut down the engines of a Horizon Air flight with more than 80 people on board has renewed attention on the mental fitness of those allowed in the cockpit.

Joseph Emerson, 44, had been flying passengers himself just three days before police said he tried to engage an emergency fire suppression system while catching a ride from Washington state to San Francisco on Sunday in the extra seat behind the pilot and first officer on Flight 2059. He was subdued by the flight crew, and the plane landed safely in Portland, Oregon.

Emerson, who has pleaded not guilty to attempted murder charges, told police after his arrest that he'd had a nervous breakdown, had been struggling with depression and the recent death of a friend, and hadn't slept for 40 hours, according to charging documents.

Emerson also said he had taken psychedelic mushrooms for the first time about 48 hours earlier. It's not clear whether he took them recreationally or in an attempt to self-medicate, but psilocybin is increasingly being recognized in the U.S. for its potential to aid mental health. The pilots and others who encountered Emerson said he did not appear intoxicated.

Here’s a look at some of the issues raised by the harrowing cockpit episode:

Airline pilots are required to renew their medical certificates regularly — annually for those younger than 40 and every six months for those older. That includes filling out forms where they are required to disclose if they have experienced depression, anxiety or drug or alcohol dependence, as well as medications they take.

The foundation of that system is trust, said Shawn Pruchnicki, a former pilot who teaches aviation safety at the Ohio State University.

“The idea is that you will confess any diseases or any problems that you have,” he said.

Pilots who do so can risk being grounded, at least temporarily, while the Federal Aviation Administration sorts out whether they're fit to fly. Pilots can also be grounded after relatives or coworkers report concerns.

Emerson had his most recent exam in September, according to Federal Aviation Administration records.

The administration started allowing some pilots on medication for mild to moderate depression to continue flying on a case-by-case basis in 2010, and some airlines have introduced confidential programs to help struggling employees. The Air Line Pilots Association also offers a round-the-clock, peer-to-peer stress hotline staffed by volunteer pilots.

“The FAA encourages pilots to seek help if they have a mental-health condition since most, if treated, do not disqualify a pilot from flying,” the agency said in an emailed statement.

Some conditions, including bipolar disorder and psychosis, are disqualifying.

Pilots who are struggling should speak up, because even if they're temporarily grounded, it's better than ruining their career and possibly costing lives with a more disastrous episode down the road, said Dr. Warren Silberman, a former Federal Aviation Administration aeromedical certification chief.

Investigators concluded that is what happened on board a Germanwings plane in 2015 when the copilot deliberately crashed the plane in the French Alps, killing 150 people.

The U.S. Department of Transportation has a mandatory drug testing program for on-duty pilots or flight attendants, which can include random testing before or after a flight, or testing based on reasonable suspicion. The tests look for opioids, cocaine, methamphetamine, marijuana and some other drugs — but not psychedelics.

The effects of psychedelic mushrooms typically last about six hours. Typically, it they no longer detectable in urine 24 hours after ingestion.

Alaska Airlines, which owns Horizon Air, said it has a zero-tolerance policy and that all gate agents and flight attendants are trained to identify signs of impairment.

The flight crew on the Horizon flight and the police who interviewed Emerson afterward said he did not appear to be impaired.

There is no specific guidance regarding pilot behavior off-duty, but Pruchnicki cautioned that drugs can show up in a random test well after the effects have worn off.

“Is that something you want to do on your days off?" he said. "And how does that fit into your mindset as a professional pilot?”

Many pilots get rides in cockpit jump seats every day as a way to shuttle between locations after making flights. Pruchnicki said he didn't think they needed to be subject to random testing because they're off-duty and not making operational decisions about the flights. Pilots can bar them from the cockpit if they present issues.

“I don’t believe that necessarily one extremely rare event means that we need to completely overhaul the entire system,” Pruchnicki said.

While psilocybin remains illegal in most of the United States, it has been gaining greater acceptance in the U.S. as a potential therapy. The Food and Drug Administration published draft guidance this summer for researchers designing clinical trials for psychedelic drugs to treat depression, post-traumatic stress disorder, substance-use disorders and other conditions.

Such hallucinogenic substances have been used by the Indigenous peoples of the Americas to induce altered states of consciousness and healing since pre-Columbian times. Users have described varied experiences, from vivid geometric shapes, patterns and colors to a sense of oneness with the universe.

Oregon became the first state to legalize psilocybin in 2020 after voters approved a measure that allowed for the manufacture and controlled, therapeutic use of psilocybin for people 21 years of age or older.

It's unclear what prompted the episode on Horizon Air — police said Emerson described having been in a dream-like state.

Brian Pilecki, a clinical psychologist in Portland who is involved in research on psychedelic therapeutics, said that for people diagnosed with psychosis or bipolar disorder, “taking a psychedelic like psilocybin can potentially trigger a psychotic episode.”

Emerson pleaded not guilty in state court Tuesday to 83 charges of attempted murder and one of endangering an aircraft.

He remains in custody and is scheduled to make his first appearance Thursday on a federal charge of interfering with a flight crew, which can carry up to 20 years in prison.