2025-09 · NASA ASRS report 2285808
Air carrier flight crew reported during pushback with the brakes applied the tow bar shear pin sheared.
We were getting ready for pushback when an uncommanded pushback occurred; which resulted in a broken shear pin. The Before Start Checklist was completed; the main cabin and flight deck doors were closed; and the aircraft was ready for pushback.Prior to the incident; we made multiple failed attempts to communicate with the ground crew via the headset. The Captain then opened his window to brief the ground crew on the hand signals we would use during pushback. From my side; I couldn't see or hear what the ground crew's reply was due to my angle of view and the loud ramp environment (running packs and APU). I could only hear and see the Captain explaining and showing them what the signals would be.I then sent an ACARS pushback request. Approximately 10 seconds later; the ground crew began pushing the aircraft without a command. At the same time; Ramp Tower was providing us with pushback instructions. I felt an initial jolt as if the aircraft was trying to move; followed by a loud snap. The Captain; through his open window; said loudly; 'What was that?' Again; I couldn't hear or see what the ground crew was saying due to the ramp environment and my angle of view mentioned earlier.I immediately contacted Ramp Tower to cancel our pushback request; stating we would call them back when ready. I noticed the parking brake was released; so I asked the Captain if he was holding the brakes. He confirmed the brakes were set and that he released them as soon as he felt that they were trying to push. The Captain then told me that the ground crew said everything looked fine and they thought we could continue.The Captain then said that he doesn't feel comfortable continuing and relying on ground crew information and would like to bring Maintenance to inspect the aircraft. I fully supported his decision and told him that I agree with him 100%. He informed the ground crew that Maintenance will need to inspect the aircraft; and then called Maintenance to explain what happened. While we waited for maintenance to arrive; I told the Captain that I think they broke the shear pin. I then opened the AOM and read the 'Broken/Disconnected Towbar' paragraph to him. Reading the AOM confirmed we made the right choice by calling Maintenance and not relying on the ground crew's assessment.The Captain then briefed the flight attendants and operations via radio. A few minutes later; Maintenance arrived. They confirmed via a working headset that the shear pin had broken and asked if the brakes were set during the uncommanded pushback. The Captain confirmed they were. Maintenance then advised that we would not be departing soon and that a further inspection was required because the brakes were set during the uncommanded pushback.After their inspection; Maintenance personnel advised that everything was satisfactory and we could continue. A new push crew with a working headset arrived and installed a new towbar. After confirming the logbook entry was cleared; we reread the entire Before Start Checklist; requested a new pushback clearance; and proceeded with the pushback normally. The flight continued without further incident.Cause: Casual factors: Late night; load and busy ramp environment; INOP headset; and limited view from the FO seat.Current AOM guidance; 'NO Headset Communication;' permits the briefing between the hand signal agent and the Captain to occur through the Captain's window. This procedure prevents the First Officer (FO) from seeing or hearing the conversation.To address this safety concern; I propose a revision to AOM guidance. The revised procedure would require the hand signal agent to come to the cockpit or approach the Captain's window through the jet bridge for the briefing on hand signals. This would eliminate noise as a factor and ensure the agent fully comprehends the signals; thus preventing any misinterpretation of the briefing as a pushback clearance. Furthermore; this change would create an additional safety barrier byallowing the FO to observe and participate in the briefing.
The push crew headset was inop. I briefed the push crew on the hand signals to be used for brake release and clearance to push. We then finished the before start checklist and sent the ACARS to push. The push crew commenced the push without a hand signal of brake release or clear to push. I called Maintenance and entered the event into the logbook. Maintenance found the shear pin was broken on the push bar but no aircraft damage was found. We then pushed and proceeded to ZZZ1 without further issues.Cause: Training for rampers to understand hand signals. Have working headsets for the push crew.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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