A Frontier Airlines plane with as many as 240 passengers onboard was swarmed by police on Sunday evening after someone spotted an ammunition magazine on the floor of the cabin, prompting a deplaning onto the tarmac as investigators carried out a security sweep of the aircraft.
The flight involved in the late-night security scare was Frontier service F9-4765 from Denver to Phoenix Sky Harbor, which was scheduled to depart just after 8 pm on May 10.
The packed Airbus A321neo being used on this service hadn’t even left the gate when a medical incident reportedly occurred on board and the crew asked for trained medical professionals to assist them in assessing the passenger.
A nurse who came forward to help was assessing the passenger when they spotted what appeared to be an ammunition magazine on the floor beside another passenger.
The flight attendants were then alerted, and the police were promptly called. The Denver Police Department had the passengers deplane onto the tarmac below and then taken back to the airport terminal, where they had to be rescreened by the Transportation Security Administration (TSA).
In a statement, a spokesperson for Frontier Airlines confirmed the incident, saying:
“As Frontier flight 4765, scheduled from Denver to Phoenix, was preparing for departure the evening of May 10, an ammunition magazine was discovered on the aircraft.”
“As a matter of precaution, passengers were deplaned and rescreened. The aircraft also underwent a security sweep with no additional findings.”
The Denver Police Department declined to comment as the FBI is the lead investigator in this incident. The FBI did not reply to a request for comment at the time of publication.
Given how late the flight was already due to depart, the subsequent delay in transporting all the passengers back to the terminal, rescreening them, and then carrying out a search of the aircraft, the pilots and flight attendants exceeded their legal duty hours for the day.
And while Frontier is based in Denver, the airline was unable to find a replacement crew to operate the flight. As a result, Frontier delayed the service overnight, with the plane only eventually taking off at 6:15 am on Monday.
A similar incident occurred on another Frontier Airlines airplane at Atlanta Hartsfield in November 2025 when a passenger discovered a loaded handgun magazine on the floor of the plane shortly before departure.
The aircraft had only recently landed in Atlanta on November 9, 2025, after a short one-hour flight from Cincinnati, and a new set of passengers was boarding the Airbus A320 airplane for its return flight back to CVG.
“A passenger on the flight discovered what appeared to be a loaded magazine containing ten hollow-point rounds on board an Airbus A320 aircraft near seat 7A,” a statement from the Atlanta Police Department explained.
The magazine was marked with the initials KH, and law enforcement is working with the FBI on the ongoing investigation.
In the immediate aftermath of the discovery, the police K-9 units, along with the TSA, Homeland Security, and officials from Atlanta’s Department of Aviation, were scrambled as all the passengers were deplaned.
And in February, a United Airlines airplane at Newark Liberty International Airport (EWR) was temporarily grounded and declared a crime scene after a bullet was discovered in an overhead bin.
It remains a mystery how the bullet came to be in the overhead bin, although all of these incidents raise further questions about the effectiveness of the TSA in preventing threats to aviation.
