A321
Flight Crew Air Transport Pilot (ATP)
Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Other / Unknown
Human Factors
Upon door closure clearance was received for push back. I contacted the push back crew and stated 'ready for push back; brakes released'. When they did not answer; I looked down to make sure I was on interphone. When I looked up; the aircraft was moving backward. The First Officer stated 'They want you to step on the bakes'. The aircraft had rolled back around 20 feet; and I eased on the brakes to stop the aircraft. The ground crew stated that the parking brake on the tug was inoperative; and they had left the tug in gear; so the aircraft parking brake was the only thing holding the aircraft still after they pulled the chocks. They changed to a tug with an operative brake and continued the push back.I thought the ground crew was on interphone; when they were not. I did not wait for a verbal acknowledgment from the ground crew before releasing the parking brake.Do not leave the tug in gear if the park brake on it is broken.
A321 Captain reported when he released the brakes ready for push back the aircraft started moving backwards. The Captain reported he stepped on the brakes and was told the tug parking brake was inoperative and they had left the tug in gear.