B737 Undifferentiated or Other Model
Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Flight Crew Last 90 Days 156; Flight Crew Total 15790; Flight Crew Type 1148
Communication Breakdown; Distraction; Confusion; Situational Awareness; Time Pressure; Training / Qualification
Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
Company Policy; Human Factors; Procedure
We were fully pushed back from Gate XX to Taxiway X tail east per ATC instructions. We are cleared to start from ground crew who were using the new remote headset. Push back was normal and per SOP. After my clearance to the ground crew to disconnect the headset; I was given the salute and I acknowledged that with taxi light per SOP and announced it to the First Officer. After engine start and accomplished after start checklist; I asked First Officer to review the bleed configuration because of the deferred MEL item that caused the air conditioner Master Caution light. As we were reviewing the maintenance release procedure; I heard a couple of banging. Not sure what the noise were; I looked outside the cockpit and noticed two ground crew were driving away from the airplane and gave us a quick wave. First Officer asked didn't we already receive the salute; and I reaffirmed the salute and after start sequencing with him.I am guessing that the ground crew returned to the airplane after giving us the salute and realized that they either forgot to remove the 'remote jack' for the headset system or the panel was not fully locked and closed.Either way; we were surprised by their presence at the airplane and not communicating to us or leaving without letting us know other than the bang we heard.This activity is actually reckless and unsafe and breaking all SOP and protocols for ground station operations. I asked First Officer to inform operation control to relate to them what had transpired. They acknowledged our report and we began our taxi for takeoff.
B737 Captain reported that ground crew approached the aircraft a second time after giving the all clear signal; resulting in a violation of SOP and a safety risk.