Mistakes in screening procedures by Transportation Security Administration employees allowed a passenger to bring two box cutters aboard a Frontier Airlines flight from Cincinnati to Tampa, Fla., the agency said on Sunday.
The passenger, a man, approached a T.S.A. checkpoint at the Cincinnati/Northern Kentucky International Airport with two backpacks around 5:30 p.m. local time on Friday.
Video footage from a review of the incident showed the man putting the backpacks and loose items in a bin for screening. The T.S.A. uses CT technology that creates a 3-D image that can be rotated and analyzed, Patricia Mancha, a spokeswoman for the agency, said.
Ms. Mancha said that the “image review capabilities of the CT were not fully used” and that the passenger’s two box cutters were not identified during the screening.
The passenger’s belongings were flagged for a further search, although it was unclear why, and one of the box cutters was then discovered. In violation of T.S.A. policy, this box cutter was returned to the passenger after its blades were removed.
“This is contrary to standard operating procedure, which requires these items to be placed in checked bags or voluntarily abandoned,” Ms. Mancha said. “The backpack containing the other box cutter, and the remainder of the traveler’s property, was screened for explosives, but the box cutter was not discovered.”
The T.S.A., which has authority over security and passenger screening at U.S. airports, prohibits box cutters in the cabin. The items are allowed in checked luggage.
The T.S.A. workers involved in the incident have been placed in a “training status for remediation on CT image review and physical search procedures,” Ms. Mancha said. The T.S.A. will conduct additional training on CT screenings in Kentucky and briefings on the incident for all screening employees nationwide.
Aboard the flight, the passenger threatened to stab passengers and crew members, said Tim Turner, a spokesman for Hartsfield-Jackson Atlanta International Airport. The plane was diverted to the Atlanta airport, where the passenger, who was not publicly identified, was taken into custody by the police, a Frontier spokeswoman said in an email.
Larry Cumberbatch, a passenger on the flight, said that he tried to talk to the man and de-escalate the situation after a woman seated next to the man notified flight attendants of the threat a little less than an hour after takeoff.
“She was saying he said he wanted to slice somebody and showed the weapon, sliding the blade in,” Mr. Cumberbatch, of Dayton, Ohio, said on Sunday.
Mr. Cumberbatch described approaching the man, who was seated before he began pacing at the back of the plane. Before long, the pilot announced that the flight would be landing soon, with no word that the plane would be headed to Atlanta instead of Tampa, the original destination, Mr. Cumberbatch said.
After the plane landed and most of the other passengers exited, the man with the box cutter attempted to leave, Mr. Cumberbatch said, adding that he heard a scuffle at the front of the plane. He said that another passenger had tackled the man and that police officers arrived swiftly after.
The Atlanta Police Department said it had helped the Federal Bureau of Investigation detain the man and referred questions to the bureau. The F.B.I. declined to comment on Sunday.
Federal prosecutors are investigating with the T.S.A. The U.S. Attorney’s Office for the Northern District of Georgia could not be immediately reached for comment on Sunday.