Date: 202008
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Light: Daylight
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Human factors: Communication Breakdown
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Other / Unknown
Detector: Person Dispatch
When detected: In-flight
Result: Aircraft Equipment Problem Dissipated; Flight Crew Overcame Equipment Problem; Flight Crew Returned To Clearance; General Maintenance Action
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: We were ready to push back from Gate XX in ZZZ for our flight to BWI. After all pushback procedures and communications were accomplished by us; [the] crew; and the Tug Driver; I asked if we could release brakes and the Tug Driver told me it was okay to release the brakes. After the brakes were released; I confirmed from the ZZZ SIP [Ramp Control] that a pushback call was not required; and just as I was about to tell the Tug Driver that he was cleared to push; the aircraft started to be pushed back. At that point I figured we had an aggressive veteran Tug Driver who knew we didn't need a pushback call and just started to push us back. After about 20 ft. into the push; the Tug Driver stopped the push. At that moment it appeared to us that the push was misguided and the tail was being pushed toward the top of the alley; Spot 4; and not the usual tail into the alley. Thinking we just had a push gone wrong; the Tug Driver then communicated to us that he would have to pull us back into the gate and recommence the push from there. After the second push was complete and the Ground Crew was released; we taxied to the runway for an uneventful takeoff and flight to BWI.Two hours into our flight; we received several ACARS messages from Dispatch and finally a phone patch. We were informed that ZZZ Operations were concerned about our pushback because it appeared; after reviewing video; that our nose wheel was turned past the 90-degree position and well beyond its limits. Dispatch asked us if we noticed any anomalies while taxiing or taking off. We replied that everything appeared to be working normally with the nose wheel and nose wheel steering. Dispatch told us to use caution when landing and taxiing in BWI and to call them when we were safely at the gate. After an uneventful landing and taxi to the gate; I called Dispatch. I was told that the initial 'misguided' push in ZZZ was no push at all but that the aircraft was actually pulling an unmanned tug into the ally. After drifting back about 20 ft.; the Tug Driver realized what was happening and he jumped on the tug and brought us to a stop. This is where the tug and towbar were pulled off by more than 90 degrees drawing operational concerns from ZZZ Maintenance.As you can imagine this came as quite a shock to the FO (First Officer) and me and raised several questions. For the Pushback Crew: Why would the Tug Driver tell me it was okay to release the brakes with an unmanned tug? Why weren't the brakes set in the tug? Why did it take over two hours to find out what happened and that a nose wheel limit had been exceeded. For me; myself: What could I have done differently to prevent or realize something was going wrong? I can't answer for the ground crew but for myself; applying some of the same techniques we use in the cockpit to other operational groups would have helped. VVMI comes to mind. Once the plane started to move without me saying 'cleared to push' would have been a good time to verify that the Tug Driver was actually pushing us back. The note for Gate XX on the ZZZ SIP [Ramp Control] about keeping the brake set until ready for pushback should have acted as a warning to be extra vigilant. Additionally; although I usually can't see the tug during pushback and I don't put my hand on the tiller until clearing the ground crew off; I will probably start putting this in my scan during pushbacks.Ground crew should actually be ready for brake release if they clear the aircrew to release brakes [and] have the brakes set and the tug manned before chocks [are] pulled. Aircrew should not accept aircraft movement until verbalizing cleared to push.




Synopsis: B737-800 Captain reported a communication breakdown between Captain and Tug Driver regarding brakes release for pushback from departure gate and resulted in improper pushback movement.