Flight Crew Last 90 Days 200; Flight Crew Total 20000; Flight Crew Type 7000
Communication Breakdown
Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Became Reoriented
Procedure
Upon pushback from gate; the tow vehicle disconnected the towbar when I was clearly asking him in accordance with ramp instructions to push deeper in the alley.  The line crew never instructed us me to set the parking brake and proceeded to disconnect the tow bar prior to my setting the brakes.  When I continually was calling him to push deeper in the alley; it felt as though the ground crew began to pull us forward against my clear instructions to continue the push.  When we started moving forward; the headset operator began to frantically call for us to set the brakes; at which point I had to immediately put the brakes on realizing that unbeknownst to myself and the First Officer that we were in fact rolling forward as opposed to being pulled forward.  I immediately got on the headset with the lineman and instructed him that we were telling him to push deeper to allow another aircraft into our gate.  The lineman reattached the tow bar and pushed us further back; at which point I clearly instructed him under no circumstances was he to allow the tow bar to be disconnected without clearly hearing me tell them that my parking brakes were set.  Somewhere in the conversation; the lineman which seemingly had an accent of some sort stated that he didn't hear me which is all the more reason that I was greatly concerned that the line people making assumptions disconnected the ground equipment nearly causing a collision on the ground with the tow truck.  This is completely unacceptable in my and the First Officer's opinion.  I just cannot imagine why they would disconnect the ground equipment when he clearly told us that he could not hear us.  The more we thought about it the more baffled we became at such a terrible situation this was due to the lineman's lack of situational awareness and how such a terrible incident was just inches away.  Again this was a total unacceptable lack of communication on the headset operator's part.
B737 Captain reports being disconnected from the tow bar by the ground crew without instructions to do so or instructions to set the parking brake. The aircraft rolls forward nearly hitting the tug before realizing the tow bar is not connected. The towbar is reconnected to push deeper into the alley per ramp instructions.