Ground personnel reported the tow bar became disconnected from the aircraft while it was being towed resulting in uncommanded aircraft movement. The brake rider applied brakes and aircraft movement was stopped.

Narrative

My team was tasked with towing Aircraft X out to Maintenance pad due to extended delay of Flight ABCD. I was the tow tractor operator and Gate number was XX. Due to a resent changes we are required to use a towbar and tractor for all tows exceeding 250 yards; this change went into effect approximately 6 weeks ago here in ZZZ. So per SOP I pushed AC (Aircraft) out like a normal push and then instructed brake rider to set parking brake which he did. We then disconnected towbar from tow tractor so as to turn tractor around and tow with my back to aircraft. After which I asked for parking brake to be released which it was and we continued our tow; in approximately 100 yards I executed a 90 degree turn to the left to follow taxi line and continued past Gates XY and XZ. once behind Gate XA I happened to hear a slight metallic noise behind me so I turned to look over my right shoulder and noticed we had a brake away and AC was veering to the left. immediately I increased speed to ensure separation and avoid AC running up on tow bar or tow tractor while instructing brake rider to SET BRAKES SET BRAKES BRAKE AWAY which he did instantly. I parked tow tractor and froze the scene; Person A was called and came out to handle the situation. Air Carrier Maintenance Control was called and they dispatched contract Maintenance to come over and inspect aircraft which they did and found no damage to tires; assembly or tow bar. We received clearance to continue tow and after switching tow bars we moved aircraft to spot without further issue.