Date: 201908
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
ATC / advisory: Ramp ZZZ
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Commercial; Flight Crew Multiengine
Human factors: Communication Breakdown; Confusion; Situational Awareness
Second reporter function: Captain; Pilot Flying
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Loss Of Aircraft Control
Detector: Person Flight Crew; Person Ground Personnel
When detected: Taxi
Result: Flight Crew Regained Aircraft Control; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Airport; Human Factors; Procedure
Primary problem: Airport

Narrative: After leaving Gate XX at ZZZ. We were being pushed to spot A. The Tug Driver stopped momentarily and we heard about a second of static on the radio. The Captain asked the Tug Driver if he said set brakes while simultaneously flashing the lights. At that point the tug and airplane began to move again. I heard a tow bar noise immediately followed by 'breakaway; breakaway'. The Captain and I instantly stepped on the brakes. The Captain then set the brakes and made sure everyone was ok. After coordinating with ramp crew; Maintenance; and Operations. We taxied back to the gate.


Second narrative: While being towed to spot A off Gate XX we experienced an uncommanded aircraft movement. Tug Driver failed to say 'set brakes' before disconnecting tow bar and the jet moved forward striking the tow bar. The First Officer and I heard a scratchy sound over the intercom; I queried the Tug Driver over the intercom asking him 'Did you say set brakes?' since I felt the jet moving and sensed something wasn't right while seeing the tug moving backwards. I immediately stepped on the brakes; turned on the taxi light; felt a thump and heard the Tug Driver say 'breakaway; breakaway'. The Tug Driver and I re-established communication. Tug Driver had the Ramp Supervisor approach the jet and we exchanged information to ensure that everyone was ok. I requested that Maintenance inspect the nose gear per AFM 3.40.1 and broke the [Maintenance Release] via ACARS. The maintenance supervisor asked me to taxi the jet back to the gate for further inspection; I had the First Officer coordinate the taxi back to the gate. I informed the Flight Attendants and passengers of the tow bar incident and proceeded to Gate XX. Passengers were given the opportunity to deplane. The First Officer and I spoke with the Ramp Supervisor in the jet bridge and shared with him the chain of events. We went down to the ramp in order to inspect the nose gear and obtain information from the Maintenance Technicians. The Maintenance Supervisor briefed me on the need to replace the 'Tow Lug' since it had scratches. Visual inspection revealed no other damage. I contacted [Dispatch] and requested that the [Chief Pilot] join the phone conversation in order to inform him of the incident and request his advice. The Maintenance Technicians released the jet back into service and I continued the flight without further incident.


Synopsis: Flight crew reported miscommunication with ground crew resulting in a tow breakaway.