NAV ERROR - THE PLT OF THIS F-16C LOST HIS TACAN AND WENT OFF COURSE AND HIS INS WAS MIS-OPERATED SO THE CTLR ASSISTED HIM.

Narrative

AFTER A TEMPORARY TOUR OF DUTY; I WAS RETURNING TO BASE IN A SINGLE F-16C. THE SORTIE INCLUDED NAV AND INST PROCS ONLY; NO TACTICAL TRAINING WAS INVOLVED. MY CLRNC RTE INCLUDED J191 FROM PATUXENT VORTAC TO SMYRNA VORTAC. I WAS TRAVELING TO THE NE ON THE JET RTE AT FL410. AFTER PASSING PATUXENT VORTAC; MY TACAN BEARING POINTER CONTINUED TO SWING PLUS AND MINUS 20 DEG IN THE DIRECTION OF PXT FOR SEVERAL MI. I SWITCHED TO INS MODE IN AN ATTEMPT TO TRACT THE RADIAL OUTBOUND. HOWEVER; MY INS MUST HAVE DRIFTED BECAUSE CTR THEN CALLED 'MIL FLT-X; TURN 20 DEGS L TO AVOID RESTRICTED AREA.' I TURNED AS DIRECTED; AND THEN WAS CLRED TO INTERCEPT J191. HOWEVER; MY ERRATIC TACAN AND FAULTY INS INFO AGAIN CAUSED ME TO DRIFT OFF J191; AND I ESTIMATE THAT I WAS 10 NM W OF J191 AT SMYRNA VORTAC WHEN I WAS CLRED DIRECT TO ALBANY. I SHOULD HAVE BEEN MORE AGGRESSIVE IN XCHKING AND UPDATING MY INS ACCURACY; SO THAT WHEN THE TACAN BECAME UNRELIABLE MY INS DATA WOULD HAVE BEEN GOOD. I COULD HAVE QUERIED ATC AS TO MY POS TO DETERMINE WHICH ON-BOARD NAVAID (IF EITHER) WAS ACCURATE; AND I COULD HAVE EASILY REQUESTED ATC ASSISTANCE IF I QUESTIONED MY NAVAIDS.