ROMULUS, Mich. – 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. 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. The three escorted off the plane in handcuffs included two men and a woman, said passenger Ilona Hajdar of Charlotte, Mich.

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, a police SWAT team boarded.

Authorities cleared the aircraft at 5:15 p.m. EDT after it was searched, the Transportation Security Administration said.

In Denver, the FBI said the North American Aerospace Defense Command scrambled F-16 fighter jets to shadow the plane “out of an abundance of caution.”