Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 201
Communication Breakdown; Human-Machine Interface; Confusion; Situational Awareness
Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Provided Assistance; Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented; Flight Crew Requested ATC Assistance / Clarification
Airspace Structure; Chart Or Publication; Manuals; Procedure
SETZR1 RNAV Departure was assigned during pushback. We briefed and ran Departure Plan Checklist and I thought the bases were covered. There was a clue during taxi; that the First Officer thought LNAV was required for takeoff. But I didn't engage him for his reasoning; we just set up for an HGS takeoff at my request. SAT Tower simply cleared us for departure on Runway 04. No additional instructions; as I recall.On departure I was flying Runway Heading as I expected. The First Officer asked me if I wanted LNAV to proceed to the first fix (VAUHN) and I said no; just runway heading. He said we were supposed to go direct and I said 'Are you sure?' He said 'YES!' So; I said ok; and we engaged LNAV and started the turn. Then he checked in with SAT Departure. They were polite as there were no traffic conflicts. They reminded us that we were supposed to maintain runway heading; (or an assigned heading; per the SID) for our clearance.In retrospect I should have asked my First Officer to go ahead and contact Departure Control in order to verify our clearance. (Let ATC be the tie-breaker.)
Air carrier Captain reported a misunderstanding between the Captain and First Officer whether to fly runway heading or comply with the RNAV Departure procedures which resulted in heading deviation.