B737-800 Captain reported a loss of aircraft control during push back from gate. Ground crew exceeded nose wheel steering angle limits and sheared pins on tow bar during push back. Captain also reported communication lapses with ground crew during event and noted wireless headsets were in use by ground crew.

Narrative

The event occurred during pushback from Gate X. I established communications with the Tug Driver via the standard script; and I was told that the 3-person Crew with wireless headsets had completed their checks and were ready for pushback. At this point the jetbridge was still attached; and I communicated this to the Tug Driver. After a minute the jetbridge was retracted and we called ZZZ Ground for pushback clearance. Once we received clearance; I released the parking brake and told the driver that pushback could commence; and asked to be told when we were cleared for engine start. After approximately 100 ft of backward movement; we hadn't been cleared for engine start; so I queried the Tug Driver. Tug Driver responded that we were cleared to start both engines; and we did so. Pushback continued; with the tail being rotated to my left toward the ZZZ '[Gate] Y'. When pushback motion stopped; I noticed that the tug was at a very sharp angle to the aircraft; almost perpendicular to the aircraft centerline on the Captain's side. After sitting stationary for about 10 seconds; I queried the Tug Driver if pushback was complete as I had received no communication from the Ground since being cleared to start engines. I received no response. The Tug Driver had briefly exited the tug and seemed to be giving some assistance to another pushback Crew Member; I could only see the Tug Driver at this point. The Tug Driver got back into the tug; and I continued to query if pushback was complete in order to set my parking brake for towbar disconnect. I still got no response. A few seconds later I realized that the aircraft was moving forward slightly; and initially it appeared to be in tandem with backward motion of the tug; as if we were being pulled. Simultaneously; I heard both the First Officer and a transmission from the Pushback Crew that the aircraft was rolling forward; as well as an urgent transmission from the Ground of 'Set your brake!' I applied pedal brakes; brought the aircraft to a stop; and set the parking brake. Immediately after this a second Pushback Crew Member ran into view and gave me a 'set brakes' hand signal. At this point I had no reason to think that the uncommanded aircraft movement had resulted in any collision with ground equipment or Personnel. I then told the Crew that I had never been informed that the push was complete; nor had I told them that the parking brake was set for tug disconnect. At about this time; a number of other Ground Ops Personnel appeared near the aircraft; apparently; they had seen the incident unfold and had tried to intervene with my Pushback Crew but were unable to get to us before the aircraft started rolling free of the tug. I established verbal communications with one of them over a headset who identified themselves as a Supervisor. The Supervisor apologized and told me that they had seen a number of errors with the pushback from their vantage point near the terminal: the position to which the aircraft had been pushed (insufficiently distant from Gate X to allow taxi out from the congested area between the '[Gate] X' and '[Gate] Y'); the sharp angle of the tug to the aircraft; as well as the failure of the Pushback Crew to communicate completion of the pushback. The Supervisor and I agreed that because of all these problems there was a possibility of nose wheel angle exceedance or other damage and that a gate return was necessary. The Supervisor asked if I wanted to be towed back into the gate or if I wanted to taxi back in. I was unsure of the state of the aircraft; so I asked to be towed. I shut down the engines and configured the aircraft for tow in. The Ground Personnel then reattached the towbar and tug to the aircraft and began to attempt a tow in. However; they had great difficulty in doing this; and I believe this was due to both the sharp angle of the tug to the aircraft as well as our proximity to [Gate] Y. After about ten minutes of attempting to tow theaircraft in; I contacted local Maintenance both to notify them of the situation and to find out if they could lend assistance with the tow in. Once Maintenance Personnel arrived; they had me set the parking brake so that they could disconnect the tug; manually move the towbar in line with the aircraft center line; then reattach the tug. They were able to then tow us back into Gate X. After speaking with both Ground Ops and Maintenance; I learned that at some point during this incident that the nose wheel angle limit had likely been exceeded as the towbar shear pin had broken and that the tow in had been performed with a second towbar. I made an aircraft logbook entry detailing what had happened; and Maintenance performed the appropriate inspection and cleared the aircraft for return to service. After consultation with my Dispatcher and the on duty Chief Pilot; we closed up the aircraft; departed the gate using a different Pushback Crew; and proceeded to our destination without further incident.