AN A320 CREW; DEPARTING DCA; WERE SLOW TO MAKE LEFT TURN UP THE POTOMAC.

Narrative

THE DCA DEPARTURE PROCEDURE STIPULATES INTERCEPTION OF THE OCA 328 DEG R. I BUILT THE RADIAL AND INSERTED IT INTO THE FLIGHT PLAN. THE FMS WAS SET TO AUTOMATICALLY INTERCEPT THE RADIAL. THE FO WHO WAS PF; AS WE TOOK THE RUNWAY FOR DEPARTURE; SET A HDG INTO THE FLIGHT CONTROL UNIT (FCU). THE EFFECT OF THIS ACTION WAS TO CAUSE THE FMS TO NO LONGER ATTEMPT TO AUTOMATICALLY CAPTURE THE VOR RADIAL I BUILT BUT RATHER TO COMMAND A TRACK EQUAL TO RUNWAY TRACK UNTIL THE PILOT 'TELLS' THE FMS TO FLY HDG. I DID NOT CATCH THE FACT A HDG HAD MISTAKENLY BEEN SET INTO THE FCU. AFTER LIFT-OFF; AT THE POINT WHERE I KNEW FROM EXPERIENCE THAT THE FLIGHT DIRECTORS SHOULD BE COMMANDING A LEFT TURN; I LOOKED AT THE FMS INDICATIONS AND NOTICED THE FLIGHT DIRECTORS WERE COMMANDING A RUNWAY TRACK NOT A TURN. I TOLD THE FO TO TURN NOW WHICH HE DID. ON RAW DATA WE WENT THROUGH THE DCA 328 DEG R BUT NOT BY ENOUGH TO HAVE FLOWN INTO THE PROHIBITED AREA NORTH OF THE AIRPORT. ATC SAID NOTHING. WE REINTEGRATED THE 328 DEG R IN SHORT ORDER. I WAS ANGRY WITH MYSELF FOR NOT NOTICING A HDG IN THE FCU WHEN NONE SHOULD HAVE BEEN SET. I ASKED THE FO WHY HE SET A HDG. HIS ANSWER SURPRISED ME: HE SAID THE LAST CAPT USED RAW DATA AND HDG SELECT TO DEPART DCA. HE THOUGHT THAT WAS 'HOW IT'S DONE.' ALL OF OUR COMPANY INFO ON DCA SPECIFIES BUILDING A DEPARTURE AS I DID; AND BRIEFING TO THE FO AS TO THE FACT WE WOULD BE USING A 'MANAGED DEPARTURE;' AS I DID. LATER; I REALIZED I RELIED TOO HEAVILY ON MY ASSUMING HE KNEW CORRECT PROCEDURES AND WOULD FOLLOW SAME.