Date: 201907
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Aircraft: A319
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
ATC / advisory: Ground ZZZ
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion; Troubleshooting; Situational Awareness
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Other / Unknown
Detector: Person Flight Crew
When detected: Taxi
Result: Aircraft Aircraft Damaged; Flight Crew Returned To Gate; General Flight Cancelled / Delayed
Contributing factors: Aircraft; Human Factors
Primary problem: Human Factors

Narrative: The tug driver cleared us to release brakes; I told him the brakes were released and we were calling for pushback clearance. It felt like he started to push us at the same time ground said push was at our discretion. We were surprised he was pushing us prior to us clearing him to do so. The First Officer pointed out someone on the ramp was trying to get the wing walker's attention to stop; when the tug did stop us. I asked the tug driver what had happened; and he said that the tug's brakes had failed and that we had rolled back. Unfortunately; the aircraft had turned and the tow bar went beyond the limit.I asked the driver why he hadn't informed us of the situation; and he said that he was desperately trying to stop the aircraft and that he had finally managed to do so. Even though we don't normally apply brakes to an aircraft that is going backwards; had he immediately told me to do so; we wouldn't risk hitting the tail as at first we were going very slow.It happened fast; but I could have asked why he was pushing without clearance; or he certainly could have told us we were rolling and to apply the brakes. I had planned on telling him that he had jumped the gun and to make sure he's cleared to push before doing so. Neither I nor the First Officer had any idea we were rolling back and dragging the tug. It felt like a normal push and I couldn't see the tug.


Second narrative: Event occurred during pushback. Tug driver told us his FOD check was complete and that it was all secure below and he was ready for pushback. Captain then released the brakes and told tug driver the brakes were released and that we would call for the push.  First Officer then called for push clearance. As I called for the push; both flight crew noticed that the airplane was pushing back from the gate. We had no communication from the tug driver that they had commenced the push. The Captain had also not said we were cleared to pushback. As we were pushing back; Ground stated that the ramp was uncontrolled and we could push at our discretion. At this point; we felt it was safer to continue the push then to have the tug make an abrupt stop. The push continued for about 50 feet off the gate. At this point; we saw a ramp worker begin waving to the left wing walker on the left wing to stop the aircraft and then he put his hands on top of his head as if the aircraft was about to hit something. At this point the aircraft stopped. The Captain tried communicating with the tug driver but did not get a response for several minutes. After approximately 3 minutes with no communication from the tug driver; he finally contacted us to let us know that he had not been pushing us back; but that the aircraft had begun rolling on its own once the brakes were released and that we were pulling the tug with us. Once the aircraft stopped; the tug was located on the Captain's side of the aircraft almost directly under his window. A Ramp Supervisor got on the headset and stated that the brakes didn't work on the tug and that was why we were moving. He also stated that the nose wheel was 90 degrees + to the fuselage of the aircraft and that it had turned past the red line markings on the aircraft fuselage. It took considerable time to disconnect the tug and tow bar from the aircraft. Contract Maintenance was involved before tug and tow bar were disengaged since the mechanic felt there was a high amount of tension on the tow bar due to the angle of the nose wheel. Once the tug and tow bar were removed; an air stair vehicle was brought to the aircraft door and the passengers were deplaned. The ground crew asked if we were comfortable with taxiing the aircraft back to the gate once the nose wheel was centered. The Captain stated he was not comfortable with that and told them we would need to be towed back to the gate. It took approximately an hour once the passengers deplaned until we were towed back to the gate. Once at the gate; the flight was eventually canceled.The ramp slopes away from the terminal. According to the ground crew; the tug brakes failed or did not work properly and once the Captain released the aircraft parking brake the aircraft began to roll away from the gate. The tug driver did not tell us he was having a problem as we were rolling backwards. It felt like a normal pushback to us. Had he stated that he was not pushing us back; the Captain could have slowly applied brake pressure to bring the aircraft to a stop. It was very fortunate that no one was injured during this roll back and that no equipment was damaged.In the future; the tug driver should immediately let the Captain know that he is not in control of the pushback. That was information that the flight crew definitely needed to know


Synopsis: Pilots reported during push back the aircraft moved uncontrollably due to tug losing its brakes.