EMB-175 flight crew reported the aircraft rolled back onto a chock during pushback when the tug was disconnected from the aircraft prior to setting brakes. Chock was removed and pushback completed.
Synopsis
EMB-175 flight crew reported the aircraft rolled back onto a chock during pushback when the tug was disconnected from the aircraft prior to setting brakes. Chock was removed and pushback completed.
Narrative
After the cockpit door was closed and locked; my FO and I ran through the Before Start Checklist; as usual. During this time the jet bridge at [Gate] XX was removed. After a couple minutes we saw a ramp agent get into the tug and pull it forward under the nose. Once the ramp agent plugged in the headset it was very loud and squeaky. I asked her to unplug it and plug it back in. The loud squeaky nose went away; however; there was still some static in the line. It was difficult to hear her but; I felt it was still clear enough to communicate. The agent and I greeted each other. I did not hear her properly give me the pushback speech; so I led the conversation by asking specifically if 'the FOD walk was complete; was the walk around done; was steering disengaged; and ready for brake release?' I heard yes each time I asked a question. I dropped the brake and told her 'parking brake was released; stand by push.' I believe it was at this point my FO turned off her ramp button and called for pushback clearance. I saw out the window that we rolled about a foot. The ramp agent said set brakes; which I immediately did. I had my FO cancel our clearance. After several minutes I saw a few station personnel standing near the nose. I opened the window and asked if something was broken? This is when I found out the tug had not been hooked up; but that the ramp agent had just wanted to pull the chocks. At this point the chock was stuck under the nose tire. Eventually maintenance was called to assist. The mechanic quickly freed the chock and reassured everyone no damage had been done. Once the chock was free; the tug was hooked up and a different set of rampers came to push us back. All in all; we were delayed about 45 minutes. I kept the Dispatcher in the loop and briefed the passengers as necessary. The rest of the flight was uneventful.I believe the static in the headsets made it difficult; but not impossible to communicate. I think expectation bias played a role. I saw the tug pull up into position so I assumed it had been hooked up. It is not standard practice for the ramper to get on the radio and ask if chocks can be removed. This has usually been accomplished already. It happens occasionally; but at this point in the process 99% of the time they are ready for pushback with the pushback speech; this is normal. From my point of view that is what I am waiting for and if the ramper doesn't give me the speech I query them and ask specifically. I think the ramp agent and myself were thinking two different things.If there is any doubt that there could be a misunderstanding due to faulty headsets; I will ask for the crew chief to come up to the jet bridge to review hand signals. I will double check that it is clear and concise for not only me; but the ramp agent as well; that they are ready for brake release.
Second reporter narrative
Event occurred at Gate XX in ZZZ. Door closure; jet bridge removal and the proper checklists and flows were accomplished. A headset was hooked up to the aircraft by the ground crew to conduct the pushback procedure. At first; when the headset was plugged in a very loud noise was being transmitted to the cockpit. After asking the ground crew to disconnect it and reconnect it; the headset still transmitted static but was clear enough to communicate. After initial greeting; the ground personnel at the tug did not go into standard pushback speech. The Captain had to lead the conversation and ask the following questions; 'Is the FOD walk complete? Is the walk around complete? Was steering disengaged?' Are you ready for parking brake release?'. All questions were answered with a 'yes' from the ground personnel. Parking brake was released. Captain said 'Parking brake released. Standby for push'. At this time; I turned off my ramp button in order to communicate with ZZZ Ramp Control to request push back clearance. I did not hear the request from ground crew to set parking brake. The Captain told me that we had rolled back about a foot and that the ground crew requested the parking brake to be set immediately. Pushback clearance request was cancelled. The ground crew informed us that the tug was not connected to the aircraft and that we had rolled back onto a chock that was now stuck underneath the nose wheel tire. Maintenance was called to assist with chock removal from underneath the nose wheel tire. No damage was done to the aircraft. A new ground crew was brought in to accomplish pushback. The rest of the flight was uneventful.I believe a lack of communication was the cause of this event. Normally by the time we are communicating with the ground crew on headsets; the chocks are removed with the hand signal request beforehand and the tug is connected to the aircraft. The information was never relayed to the flight crew. The ground crew needs to communicate with the flight crew if they are not ready for brake release.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.