In June 2015, a United Airlines FFDO threw live ammunition in the trash before eventually deciding to flush it down the lavatory toilet on an international flight from Houston to Munich.
In February 2017, a Southwest Airlines FFDO disembarked a plane in Phoenix, Arizona, leaving a loaded firearm unattended in the cockpit, after the FFDO was accused by a flight attendant of watching footage from a camera hidden in the airplane's lavatory.
In August 2022, a Delta Air Lines FFDO allegedly used his firearm to assault and intimidate a fellow crew member in response to a possible diversion of the aircraft due to a medical situation.
Liam Neeson was an air marshal in Flight lol. Although that was supposed to be a ‘serious’ movie about undercover agents rather than pilots
Air marshals were involved in the plot of Stallone's Cliffhanger. I think it's a very enjoyable, very stupid action movie.