B737 air carrier crew reported uncommanded aircraft movement during pushback. Once the crew became aware of the unintended aircraft movement; the Captain set the brakes and no injury or damage occurred.
Synopsis
B737 air carrier crew reported uncommanded aircraft movement during pushback. Once the crew became aware of the unintended aircraft movement; the Captain set the brakes and no injury or damage occurred.
Narrative
After positive communication from the flight deck to ground personal in ZZZ at gate X; at the time of departure the ground personal stated that we were waiting for a tug to get to the aircraft for pushback. The Captain said the brakes are set and to get back to us when we are all hooked up and ready to go. once a tug was found and brought to us; the ramp again communicated to the flight deck via the Captain that we were ready. I then was instructed to call ramp for a push. we got instructions to push 'tail east abeam our gate.' Shortly after getting clearance by ramp personal to start the engines; we also received the close out information which was evaluated by me and accepted correctly. I then began the engine start process as normal. it is to note that during the push back we both noticed and crew in a van follow us during the push back for no reason. with four personal in total by the aircraft; two in tug; two walking outside. During the second engine start; we both noticed that it sounded like ramp personal either pushed the push to talk or the interphone plug became disconnected. I cautiously and judicially monitored aircraft movement while also monitoring the engine start parameters. I quickly accepted the engine start process was within the normal range; I double checked both our interphone system was set correctly; and redirected my attention to the alarming movement of the aircraft not being consistent with what we were instructed; told; and directed. The aircraft moved about 3 feet before I noticed the tug come into vision in the windshield where the tugs rate of movement did not match the aircraft movement. I confirmed the tow bar connection visually was attached to the tub and I knew then we had been released without correct or safe visual and interphone communication. I spoke up to the captain that ' I think they have us disconnected we should set the brakes.' In effort to make visual connect with ground personal; I made direct eye connect with sound one in the van that followed the aircraft during the entire push back process. I may the appropriate hand gestures that the brakes were released; where he then responded to set the brakes. I verbally stated again that we needed to set the brakes the captain; which is where I as cautiously as I could; in the interest in the abundance of safety; used my side of the brakes to stop the aircraft from further movement. The tug and tow bar had been in complete view at this point where I verbally and visually said the brake are set by hold the brakes at the stops. the tug drive shrugged their shoulders and drove off as did the van that followed the aircraft that when the braking brake was set and in concision; the ground personal detaching the tow bar and interphone I believe slowly walked toward the starboard side away from the aircraft to the gate.Cause: Lack of tow trucks. Lack of proper training between what a positive communication from the ground and flightdeck means. We can get the speech we need for the push back but how useful is it if we can identify if us or them are being listen to.Suggestions: I am proud that my situational awareness was as highly trained as it was to have made a positive impact to aviation safety and human injury. Nothing can replace two personnel in the flight deck with the training and proficiency as high of a standard that I represent for Company X and for myself. Although very similar situations have happened in my experience in my past airlines; with a break away procedure taught to both pilots and push back procedures taught to both pilots; this was self-evident of good communicaton; and crew resource management is irreplaceable to aviation safety for decades to come. I am glad my quick actions and creative thinking made a positive impact to safety as this could have gone much worse. Updating this website to fill these out will help to as i could not have done this unless at a desktop. while the iPad works to; the functionally or programming is not for IOS devices; its a desktop overlay that doesn't work that well.
Second reporter narrative
The instructions from ramp when we were cleared for pushback from [Gate] X in ZZZ was tail east abeam the gate. This was communicated with the ground crew through the interphone and with brakes released they started the push. After a few seconds they said cleared to start engines through the interphone which I verbally responded to. They pushed us back; turning our tail East till we got on the line then he came to a stop. I heard nothing verbally through the interphone nor saw anything outside from the girl holding the wands so I assumed he was going to pull us forward a bit. Meanwhile we were still starting our second engine. After about another 30 seconds or so I saw that we were still not moving and that I still hadn't received the set brakes call from ground. So I made a call to ground to see if they were there. After no response I then looked down to verify that I still had the interphone selected and didn't accidentally disconnect it somehow. When I looked back up I noticed that the tug was moving forward and we were too. Initially I thought he was now moving us forward a bit before disconnecting. Then I quickly noticed that something didn't look right; we were both moving at different rates. It was then that I realized that we were disconnected and we were rolling on our own. The FO hit the toe brakes before I got there and stopped our progress. I then engaged the parking brake and looked outside like what the heck? The tug continued to drive away and the lady holding the wands gave me a dirty look before walking away. No damage occurred during this incident as the aircraft didn't hit anything during its roll. However it is a serious safety concern if the ground crew is disconnecting before receiving POSITIVE verification from the Captain; no matter how much time has passed by. During this whole time I never got a verbal or visual signal to set the brakes nor did I ever communicate in return that they were set. I asked the FO if he ever got a signal to set the brakes from his side and he did not. After debriefing the situation among ourselves verifying we just simply rolled forward a few feet and didn't hit anything; we completed the after start and continued.Cause: Ground crew disconnecting the towbar without any visual or verbal communication from the Captain that the brake was set. Suggestions: Ground crew needs to have positive verification that the brake is set before disconnecting.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.