Narrative:

We were being pushed back for engine start. We had trouble with hearing the push back crew so we delayed the engine start until we had the brakes set. The crew unhooked the tow bar and we soon realized that the aircraft was slowly rolling backwards towards the edge of the ramp. We had no sense of movement and scratchy audio with the pushback crew. I tried to reset the parking brake while both of us were stepping on the brake pedals. I then reached up and turned on the yellow hydraulic pump. The aircraft came to a stop. We verified that the aircraft's right mains were on the grass. The ground crew attempted to pull the aircraft forward with no luck. I then asked them if it would help if we powered out; we started both engines and pulled forward; stopped and had the ground crew inspect the aircraft. They said that only the right mains excited the edge of the ramp. I then asked my first officer to call operations and report the incident. I then called dispatch and told them. At first we did not realize the severity of the incident and we taxied to be deiced. While being deiced I then called maintenance control to get them involved. At that time they advised to go back to the gate.during my preflight I checked the accumulator and noticed that the it was just at the bottom of the green band; and was satisfied with the pressure. During the incident we turned on the electric pump and brought pressure up which helped stop the aircraft. After we got back to the gate and shut the engines down we noticed that the accumulator was losing pressure quickly and had dropped out of the green band. We suspect a faulty brake accumulator.

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Original NASA ASRS Text

Title: A319 flight crew experienced a brake failure after pushback but prior to engine start. This resulted in the right main gear departing the ramp and sinking into soft earth. The crew ultimately returned to the gate after using engine thrust to get back on the ramp.

Narrative: We were being pushed back for engine start. We had trouble with hearing the push back crew so we delayed the engine start until we had the brakes set. The crew unhooked the tow bar and we soon realized that the aircraft was slowly rolling backwards towards the edge of the ramp. We had no sense of movement and scratchy audio with the pushback crew. I tried to reset the parking brake while both of us were stepping on the brake pedals. I then reached up and turned on the yellow hydraulic pump. The aircraft came to a stop. We verified that the aircraft's right mains were on the grass. The ground crew attempted to pull the aircraft forward with no luck. I then asked them if it would help if we powered out; We started both engines and pulled forward; stopped and had the ground crew inspect the aircraft. They said that only the right mains excited the edge of the ramp. I then asked my First Officer to call operations and report the incident. I then called Dispatch and told them. At first we did not realize the severity of the incident and we taxied to be deiced. While being deiced I then called Maintenance Control to get them involved. At that time they advised to go back to the gate.During my preflight I checked the accumulator and noticed that the it was just at the bottom of the green band; and was satisfied with the pressure. During the incident we turned on the electric pump and brought pressure up which helped stop the aircraft. After we got back to the gate and shut the engines down we noticed that the accumulator was losing pressure quickly and had dropped out of the green band. We suspect a faulty brake accumulator.

Data retrieved from NASA's ASRS site as of April 2012 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.