B737 Undifferentiated or Other Model
Communication Breakdown; Situational Awareness
Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Other / Unknown
General Maintenance Action
Airport; Human Factors; Procedure
After normal push off [the] gate into the alley; the captain advised the tow tractor driver that he had been instructed by the tower to have the ramp crew tow the aircraft forward to clear the area behind the aircraft for another aircraft to be pushed off of the gate. The tractor driver gave a single hand up; fist closed followed by pointing over his head to indicate that he was going to move the aircraft forward. The wing-walkers misinterpreted this signal to be a simple brakes locked signal and disconnected the tow bar.After disconnecting; the tow driver signaled again to the wing-walker that they needed to tow the aircraft forward so he went to hook the tow bar back to the aircraft but it began to roll forward.The wing walker immediately stopped and moved away from the aircraft with the tow bar while the tractor driver put the tow tractor in reverse and backed away from the approaching aircraft while telling the cockpit via the head set to 'set brakes'. The tractor driver repeated the instruction to set brakes at least two more times before he received a response from the cockpit asking if there was a 'break-away'. The tractor driver responded yes and the aircraft brakes were set.The aircraft departed without further incident. There was no damage to the aircraft or any ground equipment and no injury to any of the crew working the flight.
I was pushing Aircraft X. While pushing the aircraft the captain asked me to pull forward to allow another aircraft to pushback. I gave the wing walker the signal that I was pulling the aircraft forward as he was disconnecting the tow bar I was yelling for him to stop I was pulling forward. He lift the handle to disconnect; I told him to put the handle back down the handle would not go back into place. I told him to disconnect from the tractor; and the aircraft started rolling forward at which time I told the captain to set his brakes. The captain asked was I pulling him forward; I said no because you have been disconnected. He was still rolling please set your brakes. He ask if it was a break away. Then he set his breaks and the aircraft stopped. I told him that the tow bar and the bypass was disconnected.My second wing walker was in the stop stance the whole time and never gave the pilot the set you brakes while the aircraft was rolling.
Ground personnel and a Captain of a B737 reported that the tow bar got disconnected without the brakes being set.