BANGOR – A military airplane performing touch-and-go landings at the airport on Monday afternoon ended a training session early because of smoke in the cockpit.

The KC-135 Stratotanker, which is assigned to the 101st Air Refueling Wing in Bangor, landed shortly after 1 p.m., according to Lt. Col. Debbie Kelley, the wing’s executive staff officer. The flight was scheduled to have three people on board, two pilots and a boom operator for the refueling mission, Kelley said.

“We always land as a precaution,” Kelley said. “They are all safe.” Maintenance crew were checking for damage.

Kelley was unable to confirm whether the air-refueling portion of the mission was completed, but she did say pilots often practice landing once the refueling training is finished. The source of the smoke still was being investigated, she said.

Guard and Bangor firefighters responded to the call, Kelley said. In the event of an emergency, Bangor’s air traffic control tower notifies rescue crews, said Todd Friedenberg, air traffic manager for Bangor’s Federal Aviation Administration tower.

“If we’re talking to an airplane and if they have a problem they will tell us directly and then we provide whatever assistance they ask for,” he said. “These things happen a lot more than people think they do.”