Passenger with box cutters on Frontier Airlines flight prompts emergency landing: TSA

A passenger on a Frontier Airlines flight who allegedly boarded the plane with two box cutters was taken into custody after an emergency landing Friday night, according to the airline and the Transportation Security Administration.

Several passengers on the flight, including military veterans and a former law enforcement officer, helped crew members subdue the man after they landed, according to eyewitnesses.

The flight was en route to Tampa from the Cincinnati/Northern Kentucky International Airport when it was diverted to Atlanta "after a passenger on board the aircraft was observed in possession of a box cutter," Frontier said in a statement.

TSA said in a statement on Saturday that the plane was diverted around 9:30 p.m. "after a disturbance involving a disruptive passenger, in possession of a box cutter was declared." Following a search, a second box cutter was found in the unidentified passenger's carry-on, according to TSA.

Atlanta police assisted federal partners in detaining the suspect, Atlanta Police Department spokesperson Officer John Predmore said. Predmore directed further questions to the FBI, which is leading the investigation.

The FBI declined to comment and instead referred ABC News to the TSA statement.

The TSA said in a statement Sunday that security checks identified one box cutter from the Frontier incident, but "the visible blades were removed from the box cutter and provided back to the passenger" -- contrary to standard operating procedure, which requires such items to be placed in checked bags or voluntarily abandoned.

The passenger went through screening at Cincinnati/Northern Kentucky International Airport, where his belongings were screening using CT technology, which creates a 3-D image that can be rotated 360 degrees for a thorough analysis, according to the TSA.

The image review capabilities of the scanner "were not fully used," and the box cutters were "not identified by the CT operator," the TSA said.

The passengers' belongings were then identified for further search, where one box cutter was discovered, and the box cutter was given back to the passenger after the visible blades were removed, according to the statement.

The backpack containing the second box cutter, and the remainder of the traveler's property, was screened for explosives, but the box cutter was not discovered, the TSA said.

The employees involved in this incident have been placed in a training status for remediation on CT image review and physical search procedures, the agency said.

No injuries to passengers or crew have been reported, the airline said. The Federal Aviation Administration, which is also investigating, said the plane landed safely "after the crew declared an emergency due to an unruly passenger."

Before the emergency landing, multiple passengers noticed the man acting erratically, eyewitnesses said.

Passenger Ben Mutz told ABC News he spoke to the person who was in the window seat next to the man after they deplaned. The passenger told Mutz that the man "flashed a box knife at me and said, 'I want to kill or I want to stab people,'" Mutz said.

Larry Cumberbatch was seated in the third row, flying from Cincinnati to Tampa to visit his son for his birthday. He told ABC News that a woman who was initially sitting in an aisle seat next to the man reported seeing "some kind of knife" and was afraid for her safety.

Flight attendants asked if anyone had any military or police background and would switch seats or go to the back of the plane, he said. Cumberbatch, a Navy veteran, volunteered to switch seats with the woman, he said.

At the back of the plane, Cumberbatch found the man leaning against the window-seat passenger with his feet up in the aisle seat, before getting up to go to the bathroom.

When the man exited the bathroom, he confronted Cumberbatch in the aisle, in what Cumberbatch described as a "showdown."

"People back there, you could literally see they’re afraid. So that's why I stood there, to give them a calming presence and let this guy know there's somebody watching, someone who you will have to deal with if you take it to the next level," Cumberbatch said.

Cumberbatch said a former law enforcement member talked to the man during the landing to calm him down.

Once the plane touched down, passengers were told to leave without taking any of their belongings, according to Mutz. He said he and others were unaware they had made an emergency landing until they turned on their phones and realized they were in Atlanta.

Cumberbatch and an Army veteran remained on the plane while the former officer helped escort the man down the aisle, he said. When police officers arrived, the man "got agitated" and the former officer gave him a warning before tackling him, Cumberbatch said.

"In my mind, he was really the hero right at that moment," Cumberbatch said.

The man was then taken into custody by police, according to Cumberbatch, who said he spoke to FBI agents following the incident.

Cumberbatch said he "wasn't surprised" that veterans responded in the moment.

"We're going to take control of any situation that we're in," he said.

The passengers on the flight were provided hotel accommodations and rebooked on a new flight to Tampa on Saturday morning.

Box cutters are banned in the cabin, but allowed in checked luggage.

TSA said it is conducting an internal review of the incident and will examine surveillance footage and "airport security checkpoint processes/operations."