DENVER (AP) - September 11, 2011 --Police temporarily detained and questioned three passengers at Detroit's Metropolitan Airport on Sunday after the crew of the Frontier Airlines flight from Denver reported suspicious activity on board, and NORAD sent two F-16 jets to shadow the flight until it landed safely, airline and federal officials said. The three passengers who were taken off the plane in handcuffs were released Sunday night, and no charges were filed against them, airport spokesman Scott Wintner said. Frontier Flight 623, with 116 passengers on board, landed without incident in Detroit at 3:30 p.m. EDT after the crew reported that two people were spending "an extraordinarily long time" in a bathroom, Frontier spokesman Peter Kowalchuck said. FBI Detroit spokeswoman Sandra Berchtold said ultimately authorities determined there was no real threat. "Due to the anniversary of Sept. 11, all precautions were taken, and any slight inconsistency was taken seriously," Berchtold said. "The public would rather us err on the side of caution than not." The Airbus 318 taxied to a pad away from the terminal, and police took the three passengers into custody, Kowalchuck said. Three passengers were escorted off the plane in handcuffs, passenger Ilona Hajdar, of Charlotte, Mich., told The Associated Press. She said she realized there was a problem when the plane's bridge didn't extend at the gate. The plane then rolled to a remote spot on the airfield. After about a half hour, police SWAT boarded. "Everybody, put your hands on the seat rest in front of you. Don't move," they said, according to Hajdar, 27, who had been asleep for most of the flight and on board with her 2½-year-old daughter. Passenger Belinda Duggan, from Troy, Mich., said those led away were two men and a woman. She said the first time she realized something was wrong was when the plane taxied by the gate and headed for a remote patch of tarmac. "I said, `Oh my God,"' Duggan said. "All of a sudden, a SWAT team went through and saying, `Please place your hands on the seat in front of you."' The police had three dogs with them, she said. After leading the tree cuffed passengers away, police asked the remaining passengers to board buses and taken to the Romulus police headquarters for interviews, Duggan said. Authorities cleared the aircraft at 5:15 p.m. EDT after it was searched, the Transportation Security Administration said. Kowalchuck said luggage was removed from the plane for inspection by police K-9 sniffer dogs. The remaining passengers were taken by bus to the terminal. Flight 623 originated in San Diego before stopping at Denver International Airport on its way to Detroit. In Denver, the FBI said that the North American Aerospace Defense Command scrambled F-16 fighter jets to shadow the plane "out of an abundance of caution." The plane was searched and nothing was found, the FBI said. Two F-16s were dispatched to shadow the Airbus, said John Cornelio, spokesman for the North American Aerospace Defense Command, which is headquartered at Peterson Air Force Base in Colorado Springs. Wintner says the Frontier flight crew radioed to request police help when the plane landed, prompting responders to greet the flight and question passengers after the aircraft taxied to a remote location at the airport. Wintner said he didn't know the nature of the security issue. Also Sunday, the 10th anniversary of the Sept. 11 attacks, NORAD sent two F-16s to escort a Los Angeles-to-New York American Airlines flight after three passengers made repeated trips to the bathroom, officials said. A law enforcement official said it wasn't thought to be terrorism. Flight 34 landed safely at New York's Kennedy Airport. New York has been in a heightened state of security after federal officials received a credible but uncorroborated tip of a car bomb plot on the anniversary in either New York or Washington. --- Anderson reported from Denver. Associated Press writers Jeff Karoub in Detroit and P. Solomon Banda in Denver contributed to this report.