B737 pilot crew reported the aircraft began to roll aft unexpectedly when the brakes were released for push back requiring a quick reapplication of the brakes resulting in an abrupt stop.
Synopsis
B737 pilot crew reported the aircraft began to roll aft unexpectedly when the brakes were released for push back requiring a quick reapplication of the brakes resulting in an abrupt stop.
Narrative
We were contacted by the tug driver after all doors showed closed and Before Push checklist completed. Time showed XA19z. Tug driver contacted us over the interphone and specifically asked us to release the parking brake 'so we can get the on-time.' I asked the tug driver if he was ready to push. He told me; 'No; we have to load a few more bags.' I told him clearly 'I can't release the parking brake until you are ready to push. Call me back when you are ready.' He said 'Okay.'About 60 seconds later; the tug driver called again; saying he was 'ready for push.' All doors still showed closed. I released the parking brake and told him 'Brakes released; do not push. We are calling for push clearance.' The time was XA20z; our exact scheduled departure time.As my FO was sending the Silent Push request via ACARS; I felt and saw that the aircraft was rolling backwards. Just as I went to apply the brakes; the tug driver said urgently; 'Set brakes! Set brakes!' I immediately applied the brakes and set the parking brake. The aircraft lurched to a stop. I announced over the interphone; 'Parking brake set.' No response from the tug driver. It is my estimation that the aircraft rolled backward about 3 feet.My FO and I then noted that the FWD CARGO annunciator illuminated. We also felt the nose raise as the push tug captured the aircraft. We were not told to release the brakes to facilitate this. Several minutes elapsed while the forward cargo door was open. The light extinguished and the tug driver reestablished contact with us via the interphone. I asked him pointedly; 'When you said you were 'ready' a few minutes ago; was the tow bar attached to the aircraft; Yes or No?' He replied clearly; 'No.' I responded with a brief admonishment; saying our SOPs are predicated on full compliance; truth and accuracy in communication. It is the fabric from which we weave a safe operation. And *we* were fortunate that no one was injured and that nothing was damaged.He responded by saying; 'This is one hundred percent my fault. I apologize.'I replied that to him that it is my professional duty to report this. Again; he apologized; taking complete responsibility for the incident.The pushback was recommenced; though the procedure was hampered by what appeared to be yet another failure of the wireless headsets. Hand signals needed to be used to complete the procedure.
Second reporter narrative
At departure time; the tug driver asked that we release the brakes; and then they would add a couple last minute bags to the forward cargo compartment. The CA informed him to let us know when they were ready to push; and he would release the brake then. After a minute or so; he said they were ready for push and asked again for brake release. CA released brakes; and we could feel the aircraft moving backwards. The tug driver told us 'set brakes; set brakes' while the Captain simultaneously pressed the brakes and set the parking brake; and we felt the aircraft lurch to a stop. At the same time as the brake was set again; the forward cargo door opened; presumably to get the late bags on. We called ramp and canceled our pushback; and waited for a response from the tug driver. He finally responded to us after the cargo door was closed and said he was ready for pushback. The CA explained to him how unsafe what just happened was and made sure he understood safety is paramount; not getting the on-time departure. The tug driver admitted it was entirely his fault and apologized several times. During the pushback; we lost communication with the wireless headsets of the push crew and needed to revert to hand signals; which unfortunately; seems to be more and more common.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.