Air carrier pilot crew and push-back tug driver reported an aircraft break-away incident. The tow bar shear pin broke during a push-back quick stop and the aircraft continued to roll. Captain applied brakes to stop the roll.
Synopsis
Air carrier pilot crew and push-back tug driver reported an aircraft break-away incident. The tow bar shear pin broke during a push-back quick stop and the aircraft continued to roll. Captain applied brakes to stop the roll.
Narrative
At the gate @ ZZZ. The Before Push checklist was complete and ground crew said they were ready; so while we were waiting to get a word in for push clearance; I released the parking break for an on time at XA10 local. I was monitoring ATC ground along with my FO (First Officer) when we received our push clearance a few minutes later: cleared to push after the Triple Seven on taxiway 1". I turned my volume down on the left radio (for ATC) per SOP; relayed the clearance to our tug crew; and after a short delay we started pushing. A few seconds later; my FO is talking to ATC ground again and tells me to stop the push. I immediately relay "stop the push" to the tug driver and we abruptly stop. It sounded like something happened to the tow bar with a loud crunching noise below; but I hear nothing from tug driver regarding this and we are still slowly moving. Quickly realizing that we broke away; I announced "break away; breakaway" over the interphone while applying the brakes just as I saw the tug appear in front of us below. Still no response from tug driver because sometime after the shear pin broke; Wi-Fi communication was lost between us and tug. We notified ATC that we were not moving for awhile; then talked to maintenance and ZZZ Ops. Eventually the tug driver reestablished comms and; in the conversation; said he had only seen the Triple behind us and thought that was our traffic.From talking to the tug driver and also ATC; best guess is that our tug driver mistook the inbound Triple that was on Bravo for the Triple that we were supposed to wait for. We did not know about them and it was not necessary for ATC to mention that traffic to us because it was not a factor."
Second reporter narrative
At XA13z we were cleared to push back onto A after a heavy 777 passes by." I repeated back 737 but was corrected by ground that it was a heavy 777. I then repeated that to ATC and told the Captain our push instructions from ground control verbatim. Ground control did not give the company name of the 777 or its direction relative to our plane. In this instance a 777 was passing behind our aircraft on taxiway 1 heading toward the terminal to park. The tug driver assumed this was the 777 he was waiting for and began the push. At XA14Z the ground controller stated Aircraft X hold; which I repeated back and then told the Captain to hold the S got relayed to the tug driver who very abruptly halted the push and broke the tow pin causing us to be separated from the tug. We came to a stop and the Captain set the brakes. At XA14 a new voice came on the ground frequency and asked if we heard their instructions which I said I did and passed them to the tug driver. He then says "if you're getting pushed onto A you're waiting for traffic on taxiway 2 not 1 and we should have communicated that to the tug driver." After 30 minutes or so we were underway uneventfully."
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.