Detroit Metropolitan Airport spokesman Scott 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.