A CL65 DEPARTING DCA DEVIATED FROM ASSIGNED TRACK BECAUSE HSI VOR RECEIVER WAS MALFUNCTIONING.

Narrative

WE DEPARTED RWY 1 DCA RONALD REAGAN NATL ARPT VIA THE DEP SID TO INTERCEPT THE 328 DEG RADIAL AND TRACK IT OUTBOUND. AFTER TKOF I TURNED TO A HDG OF 310 DEGS TO INTERCEPT THE OUTBOUND 328 DEG RADIAL PER DEP PROC. DURING THE CLB WE BEGAN TO RECEIVE SEVERAL ERRATIC INDICATIONS ON THE HSI IN GREEN NEEDLES; BUT WAS UNAWARE IF THIS WAS DUE TO THE CLOSENESS OF THE VOR AND POSSIBLE ZONE OF CONFUSION INDICATIONS. WE NEVER ESTABLISHED ANY TRUE SIGNAL AND CONTINUED OUR INTERCEPT HDG OF 310-320 DEGS TO STAY L OF THE RIVER OR W OF P-56. THE FO WAS MONITORING OUTSIDE THE ACFT VERIFYING THAT WE STAYED JUST TO THE W OF THE RIVER. AT 1500 FT MSL OR 5-6 NM FROM ARPT; WE BEGAN COMPLYING WITH THE PROPER CLB NOISE ABATEMENT PROCS AND TRYING TO FIGURE OUT WHAT WAS WRONG WITH OUR NAVAIDS. AT THIS POINT THE ATC CTLR (POTOMAC DEP) INQUIRED ON OUR HDG AND WE STATED IT WAS 310 DEGS. HE ASKED IF THIS WAS ASSIGNED AND IF SO WHO ASSIGNED IT. THE FO ON THE PNF STATED NO THIS HDG WAS KEEPING US JUST L OR W OF THE RIVER. THE CTLR THEN ASSIGNED US A HDG OF 340 DEGS WHICH WE COMPLIED WITH. THIS INDICATED TO US WE MAY HAVE COMPENSATED TOO FAR TO THE W OF THE RIVER OR COURSE. DUE TO OUR WORKLOAD; TASK; AND SHOCK THAT WE MAY HAVE OVERCOMPENSATED TOO FAR W TO ENSURE ADEQUATE SEPARATION OF P-56; WE REALIZED AFTER CHANGING FREQS AND CTLRS THAT WE SHOULD HAVE RPTED OUR NAV ISSUE. TO HELP AVOID THIS TYPE OF SITUATION; OUR NAVAIDS SHOULD HAVE BEEN BACKED UP WITH FMS ON OUR PDF SCREENS WITH THE FIX PAGE ALSO INDICATING THE RADIAL DRAWN OUT ON OUR DISPLAY TUBES. ALSO; A QUICKER RPT TO ATC THAT NAV/AID PROBS AND REQUEST OF A HDG WOULD HAVE BEEN BETTER.