Narrative:

This was day 2 with a double red eye flight. Aircraft was ready for pushback in area X in ZZZ. Before start checklist was completed and we were cleared to 'release parking brake' by the tug crew. There was major congestion in the ramp and an aircraft X was waiting to be parked behind us. It was a good 5 minute wait when the tug crew said; 'since we are waiting; can we load 5 more bags that just showed up' I agreed to the request. We noticed the cargo door open on the door page. After a couple minutes I queried the tug driver how it was going. No reply. Then the first officer exclaimed - 'we're rolling' (the aircraft was rolling forward due to a slight incline) on hot mic I said 'cockpit to ground in a loud voice'; no reply. I then aggressively stepped on the brake pedals before the tug and airplane ran into a 6 foot concrete wall / berm. The maneuver was very noticeable to anyone on the aircraft. We probably rolled 8-10 ft. Before stopping and came within 5 feet of the tug hitting the concrete wall. Shortly after incident; the tug driver/ supervisor answered me on the hot mic. He apologized profusely. Apparently the tug driver/ supervisor left the tug unattended to help load the bags without communicating to the flight crew. The parking brake on the pushback tug failed and aircraft began to roll forward. Gate return; performed after landing checklist and had maintenance inspect for nose wheel damage. (Log book write up.) fortunately; no damage was found and we departed for ZZZ1 about an hour late. Have more staff at stations. Also nonstandard leaving a tug with aircraft under the tug driver control. My understanding is when I release the brake as instructed. The tug driver is in charge of the movement of the aircraft.

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Original NASA ASRS Text

Title: Airbus pilot experienced aircraft commanded movement due to tug brake failure. Aircraft was undamaged.

Narrative: This was day 2 with a double red eye flight. Aircraft was ready for pushback in Area X in ZZZ. Before start checklist was completed and we were cleared to 'release parking brake' by the tug crew. There was major congestion in the ramp and an Aircraft X was waiting to be parked behind us. It was a good 5 minute wait when the tug crew said; 'since we are waiting; can we load 5 more bags that just showed up' I agreed to the request. We noticed the cargo door open on the door page. After a couple minutes I queried the tug driver how it was going. No reply. Then the First Officer exclaimed - 'we're rolling' (the aircraft was rolling forward due to a slight incline) on hot mic I said 'cockpit to ground in a loud voice'; no reply. I then aggressively stepped on the brake pedals before the tug and airplane ran into a 6 foot concrete wall / berm. The maneuver was very noticeable to anyone on the aircraft. We probably rolled 8-10 ft. before stopping and came within 5 feet of the tug hitting the concrete wall. Shortly after incident; the Tug Driver/ Supervisor answered me on the hot mic. He apologized profusely. Apparently the Tug Driver/ Supervisor left the tug unattended to help load the bags without communicating to the flight crew. The parking brake on the pushback tug failed and aircraft began to roll forward. Gate return; performed After Landing Checklist and had Maintenance inspect for nose wheel damage. (Log book write up.) Fortunately; no damage was found and we departed for ZZZ1 about an hour late. Have more staff at stations. Also nonstandard leaving a tug with aircraft under the tug driver control. My understanding is when I release the brake as instructed. The Tug Driver is in charge of the movement of the aircraft.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.