Midair mix-up results in air marshals detained, investigations by 2 federal agencies

Passengers on United Flight 3531 from Newark, N.J., to Minneapolis got a big surprise after the wheels hit the runway at Minneapolis-St. Paul International Airport late Monday night.

Instead of taxiing straight to the gate as planned, the small regional jet wound up waiting far from the terminal as groundworkers pulled up with a set of portable stairs, police in tow.

On a recording captured by LiveATC.net you can hear the MSP tower telling the crew that the help they'd called for was on the way.

"3531, the air stairs and the PD are moving now, if you want to inform the flight attendants to disarm the doors."

The crew apparently did not know that two air marshals were aboard the plane. A flight attendant raised the alarm after spotting a gun on one of them.

Twin Cities airport spokesperson Patrick Hogan said officers met the plane on the tarmac.

"Police responded to the aircraft, boarded the plane, and detained two individuals, who were escorted to the police operations center for questioning by the FBI," Hogan said.

FBI Special Agent Cindy Burnham said her colleagues cracked the case in no time, but they're still trying to figure out why they had to get involved in the first place.

"Their identities were confirmed as air marshals on the ground, and the FBI is investigating how this happened, and we're working with TSA and the airline to ensure that it doesn't happen again," Burnham said.

For its part, the Transportation Security Administration said in a statement that "protocols for notification of law enforcement presence aboard an aircraft are in place to avoid incidents like this."

The TSA said it's working with the carrier to figure out what happened.

Indianapolis-based Republic Airline — which operates the flight on behalf of United — said in its own statement that it's aware of the incident and is working with investigators.