Minneapolis ? Two Northwest Airlines pilots failed to make radio contact with ground controllers for more than an hour and overflew their Minneapolis destination by 150 miles before discovering the mistake and turning around.

The plane landed safely Wednesday evening, apparently without passengers realizing that anything had been amiss. No one was hurt.

The Federal Aviation Administration said the crew told authorities they became distracted during a heated discussion over airline policy and lost track of their location, but federal officials are investigating whether pilot fatigue might also have played a role.

The National Transportation Safety Board does not yet know if the crew fell asleep, spokesman Keith Holloway said, calling that idea “speculative.”

The pilots didn’t become aware of their situation until a flight attendant contacted them through an intercom from the cabin to the cockpit, said a source familiar with the investigation who wasn’t authorized to speak publicly and asked not to be named.

Flight 188, an Airbus A320, was flying from San Diego to Minneapolis with 144 passengers and five crew. The pilots dropped out of radio contact with controllers just before 7 p.m. CDT, when they were at 37,000 feet.

The jet flew over the airport just before 8 p.m. and overshot it before communication was re-established at 8:14 p.m, the NTSB said.

The FAA notified the military, which put Air National Guard fighter jets on alert at two locations. As many as four planes could have been scrambled, but none took to the air.

Andrea Allmon, who had been traveling from San Diego on business, said no one on the plane knew anything was wrong until the end of the flight.

“Everybody got up to get their luggage and the plane was swarmed by police as we were getting our bags down from the overhead bins,” she said.

She said they were kept on the plane briefly while police talked to the crew, then allowed off. She said she was “horrified” to learn what had happened.

“When I do my job I do my job,” she said. “These guys are supposed to be paying attention to the flight. The safety of the passengers should be first and foremost. (It’s) unbelievable to me that they weren’t paying attention. Just not paying attention.”