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.

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Original NASA ASRS Text

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

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.

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.