ERJ 175 flight crew reported the aircraft began to roll straight ahead during push back. The Captain applied brakes to stop the aircraft and the flight crew determined they had not been told by ground crew that the tug had been disconnected.
Synopsis
ERJ 175 flight crew reported the aircraft began to roll straight ahead during push back. The Captain applied brakes to stop the aircraft and the flight crew determined they had not been told by ground crew that the tug had been disconnected.
Narrative
This was our second push back for the flight. The first time we had a Maintenance issue and had to return. After Maintenance was able to fix the issue we were pushed back a second time; all communication during the initial push back was standard and without issue; headsets were working and all communication was clear. During the push back we were told via headset clear to start engines; I replied starting engine 1. I continued to monitor outside while asking my First Officer (FO) to start engine #1. FO stated good start # 1. We were pushed back at an angle to the line and I was expecting to be pulled to the right to align us on the alley line; at this time two of the ramp crew walked away to the aircraft left and back to the gate. I saw the tug going to the right of the nose and the aircraft began to roll straight ahead. This immediately did not feel right and I asked if we were still connected. It was getting no immediate response I applied both pedal brakes and smoothly but quickly applied the parking brake. The aircraft stopped rolling and myself and the FO had a dialogue to verify that the tug had in fact been unhook and was pulling away without any verbal communication or signals. We were never told to set brakes and never told the ground crew they were clear to disconnect. Ground crew simply unhooked the tug and left. We rolled approximately less than 10 ft. I do believe had myself and my FO not been vigilant and situational aware this could have resulted in an accident or incident. I called ZZZ operations and notified them of what happened. They sent out the Supervisor who had done our push back and was told all was good on their end and that the airplane was clear to depart if we had no other issues; they also gave us a thumbs up signal. We continued on to our destination without further issues.
Second reporter narrative
ZZZ ground crew with many trainees disconnected tug without communicating to flight deck to set parking brake - aircraft rolled forward until Captain applied parking brake. Out of gate at ZZZ; under night operations; we pushed back from the gate. The ramp was not well lit. During the pushback; the Captain; noticing the large number of orange vested trainees; out of an abundance of caution; wisely elected to hold off on starting the first engine until we were disconnected and all the personnel were clear of the aircraft (this info I present here just to establish that the number of trainees was significant enough to register as a concern by the Captain). During this disconnect; I personally noticed that it appeared there were multiple people being trained at the same time. Ground personnel disconnected; and we waited and even discussed the fact that one of the trainees was standing to the side still holding red X and no one had saluted and waved off. I saw that a trainer then instructed the trainee to drop the red X and salute; which they did; and the ground personnel departed. After the engine start; we experienced a problem with hydraulic SYS 2/Nose wheel steering and after a discussion with maintenance; it was decided we should return to the gate. We shut down #1 and waited for the ground crew to return and tug us back to the gate; which went normal. After maintenance came and trouble-shot the problem; we pushed back again. This time; when the ground crew said we were cleared to start number 1; we did so. The tug had pushed back and then pulled us forward at an angle to the taxi-out line. We stopped; still at a slight angle to the taxi-out line. After the engine start; I called up the hydraulic status page; and we were discussing the hydraulic indications when I had the sensation of acceleration forward and also noticed out of my peripheral vision that we appeared to be moving forward again. For a second I thought the tug had stopped and then was moving us again; but it definitely didn't feel 'right' - not like a normal tug movement. At that point we had not heard anything from the ground crew after we were cleared to start engines. Then I also noticed the tug moving away from the nose to the right. Again; it was very dark; but the thought was forming that the ground crew had disconnected us without communicating this or having the Captain set the parking brake. As my brain simultaneously decided to reach my feet forward and apply the brake pedals and say something to the Captain; Captain had come to the same conclusion and applied the parking brake; stopping us after we had moved approximately 10 or 15 ft. There were still ground personnel around the aircraft and the tug was at that time crossing back in front of us. If the Captain had not applied the parking brake when they did; I think it's a high likelihood that a serious incident could have occurred. Captain and I discussed what happened and we had gone through the same confusion of sensation - the mental disconnect of why it felt like the airplane was moving when as far as we knew it shouldn't be (kind of like the sensation one gets when the jet bridge moves away). The Captain then called operations and told them what had just happened so the ground crew could get some immediate feedback. After this; we proceeded with the flight as normal. I think this may have occurred is that there may have been too many inexperienced ground crew on the team and too much training going on at the same time; causing a generally chaotic feeling during the pushback; especially at night. Look at limitations on number of personnel being trained at any one time.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.