AN NBC TRACON CTLR RPTED THAT A C340 PLT BECAME DISORIENTED AND ENTERED THE PATTERN AT NBC WHEN HE HAD BEEN INSTRUCTED TO ENTER THE PATTERN AT HXD. THE CONFUSION OF THE C340 PLT CAUSED AN NMAC WITH AN F18 IN THE NBC PATTERN.

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A C340; WAS ATTEMPTING TO LOCATE HILTON HEAD ARPT; HILTON HEAD ISLAND; SC (HXD). THE PLT CONTACTED HXD CTL TWR ESTIMATING HIS POS 'APPROX 17 MI N' INBOUND TO LAND. HXD TWR INSTRUCTED THE PLT TO ENTER A L DOWNWIND FOR RWY 3 AT 1200 FT. HE MADE A TURN TOWARD MARINE CORPS AIR STATION BEAUFORT; BEAUFORT; SC (NBC); FROM A POS 5 NM E. THE ACFT CROSSED LESS THAN 1 MI OFF THE DEP END OF RWY 5 AT NBC AT 1200 FT AND ENTERED A L DOWNWIND FOR THAT RWY. AT ROUGHLY THE SAME TIME A FLT OF 2 F18'S WAS BEING CLRED FOR TKOF FROM RWY 5. JUST AS THE F18'S WERE CLRED FOR TKOF AND SWITCHED TO DEP CTL; THE LCL CTLR IN NBC TWR LOOKED AT THE TWR RADAR DISPLAY AND OBSERVED THE CONFLICTING TFC. THE TFC COULD NOT BE OBSERVED VISUALLY BY TWR PERSONNEL. ACCORDING TO PROC; THE F18'S CONTACTED ME ON DEP WHILE ON TKOF ROLL AND I CALLED TFC. THE F18'S PASSED RAPIDLY DOWN THE L SIDE OF THE CESSNA; CLBING. AS THE C340 CROSSED THE DEP END OF THE RWY; THE PLT REALIZED THAT HE WAS NOT IN THE PATTERN AT HXD AND ADVISED HXD TWR THAT HE BELIEVED HE WAS AT THE WRONG ARPT. THE LCL CTLR AT HXD TWR STATED; IN A PHONE DEBRIEF; THAT HE BELIEVED THAT THE C340 WAS SHOOTING AN APCH TO AN ABANDONED AIRFIELD AT PARRIS ISLAND; 9 NM N OF HXD; AND TOLD THE PLT TO CONTACT BEAUFORT APCH. THE PLT ATTEMPTED TO CONTACT ME ON THAT FREQ AND I TRIED TO RESPOND. HIS XMISSIONS WERE BROKEN AND BARELY INTELLIGIBLE. THE PLT DID NOT SPEAK AFTER I RESPONDED TO HIM. WHILE ATTENDING TO OTHER DUTIES; HE CALLED A FEW MORE TIMES AND TO EACH CALL I RESPONDED AT LEAST ONCE. COMS AND RADAR IDENT WERE ESTABLISHED WITH THE C340 WHEN HE RPTED HIS POS 'ABOUT 17 NM NW' OF HXD AT 1200 FT. IN HIS POS HE WAS 6 NM SW OF NBC; AND 2 NM L OF THE RWY 5 APCH COURSE; HEADED SE. THERE WERE SEVERAL TACTICAL JETS CONDUCTING IFR APCHS TO RWY 5 AT NBC. TFC WAS CALLED ON AN F18 AT 12 O'CLOCK POS; LESS THAN 1 MI; SAME ALT. THE C340 CALLED THE TFC IN SIGHT AND THE PLT OF THE F18 EXECUTED AN EVASIVE MANEUVER TO THE R TO AVOID COLLISION. RADAR TARGETS CAME WITHIN A QUARTER OF A MI. THE LCL CTLR AT NBC STATED; AFTER THE FACT; THAT BY THAT TIME HE HAD THE C340 IN SIGHT AND 'COULD HAVE NOT COME CLOSER' TO THE F18 ON FINAL. THE RADAR CTLR WORKING THE F18 STATED THE SAME. THE C340 PLT WAS ADVISED OF HIS INFRACTION AND ADVISED TO CONTACT HXD TWR FOR LNDG INSTRUCTIONS. HE LANDED AT HXD WITHOUT FURTHER INCIDENT. HE THEN CALLED NBC TRACON TO ACKNOWLEDGE HIS MISTAKES AND WAS VERY APOLOGETIC. IT WOULD SEEM THAT IF THE PLT HAD BEEN MORE OBSERVANT TO VISUAL CUES; SUCH AS THE LAYOUT OF NBC AS OPPOSED TO THAT OF HXD; AND THE ARPTS' LOCATIONS IN RELATION TO THE ATLANTIC OCEAN; THIS MIGHT NOT HAVE HAPPENED. NBC HAS INTERSECTING RWYS 5/23 AND 14/32 -- HXD HAS ONLY RWY 3/21. NBC IS 15 MI FROM THE BEACH -- HXD IS PRACTICALLY ON IT.