B787-900
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 133; Flight Crew Total 11947; Flight Crew Type 1417
Ground Event / Encounter Loss Of Aircraft Control
Flight Crew Regained Aircraft Control
Equipment / Tooling
Aircraft X was repositioned from Gate XX to a hard stand; to open gate XX for another arriving aircraft; and to finish a maintenance deferral for a ELEC APU STARTER R status message we had at the gate before departure. We received our new [release] and accomplished the Before Push Checklist. The tug operator stated he was ready for push pull from our position. We requested and received clearance to begin the push pull and asked the tug operator if he was ready again. He stated brakes release with I responded brakes released cleared to push pull. I noticed forward movement the same time the tug operator did and applied the parking brake. The tug operator stated his tug malfunctioned and released the aircraft. The tug operator also stated to our Operation Personnel at the aircraft that the tug malfunctioned. The tug operator stated aircraft movement about 30cm to 35cm but seemed further. The aircraft nose wheel did not contact the tug or anything else during movement. Operations and Maintenance was notified and Maintenance performed an inspection of the nose gear and the main gear. They replaced that tug with a new tug and performed a normal push pull from the hard stand for taxi.
B-787 Captain reported uncommanded aircraft movement during pushback.