B787 flight crew reported aircraft rolled uncommanded during pushback after brake release and prior to tug connection. Captain set brakes and stopped aircraft.
Synopsis
B787 flight crew reported aircraft rolled uncommanded during pushback after brake release and prior to tug connection. Captain set brakes and stopped aircraft.
Narrative
Aircraft Movement: During our aircraft's positioning on the [maintenance control] ramp at ZZZZ; a unique ground scenario unfolded. Despite completing preflight checks and initiating 'Before push steps and after permission granted to release parking break' the aircraft began moving slowly after the brakes were released. Notably; the ramp personnel did not communicate the movement to the crew. The crew identified the issue; stopped the aircraft; and continued with the engine start. It is Important to note due to restrictions; Crew was dropped off at door two left of the aircraft. Flight Crew was not aware that a tug was not connected to the plane. To prevent such situations; it's crucial to recognize the technical threat of the parking brake needing to be set throughout ground ops until ready to taxi as in operations tugs may not be connected to the aircraft to hold the plane once breaks are released. After speaking with the flight crew; we all suggest incorporating verbiage in the FM (Flight manual) and FOM brake release procedures to address this. Additionally; for immediate awareness; the Briefing in Content should highlight this threat for similar future operations.
Second reporter narrative
We were positioned on the [maintenance control] ramp at ZZZZ for engine start. We were expecting No Headsets would be available for engine start; and so were anticipating a briefing with the Ramp agent. However; we were informed that they would indeed have a headset. The ATIS was reporting that the departure RWY (runway) was wet; our Take Off Data indicated that TO was not possible on wet runway.The doors were closed; the flying FO (First Officer) performed his Before Push Flow; and the Before Push Checklist was completed. The ramp agents gave CA (Captain) the chocks removed" sign. The Captain told the ramp he was releasing the brakes; the Ramp Agent asked us something about "Pressurizing". Meanwhile we received 2 Final Weights Manifests.I was in the center jumpseat and was working with the flying FO to get our Take Off data; and coordinate with Base OPs to confirm the RWY was indeed dry.The aircraft began to move so slowly that I did not feel the movement; and from my seating position nor did I see it. Fortunately the other [Relief Pilot] did notice we were moving; told the Captain who then reset the parking break. The ramp personnel on headset did NOT notify the crew that the aircraft had moved; I do not believe we moved more than a few inches."
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.