ATR72 CREW LANDED AT AN ARPT OTHER THAN THE INTENDED DEST.

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DURING A SCHEDULED FLT FROM DOMINICA TO ST LUCIA; IT WAS THE FLC'S UNDERSTANDING THAT HEWANORRA WAS OUR PROPER DEST FOR ST LUCIA. (FIRST FLT TO ST LUCIA FOR BOTH FLC.) AFTER RECEIVING CLRNC FOR APCH (VOR/DME 10) AND CLRNC FOR LNDG AT HEWANORRA; WE TAXIED THE ACFT TO ASSIGNED GATE. AT THE GATE; NO RAMP ASSISTANCE WAS PROVIDED TO PARK THE ACFT; BUT GND PWR AND AIR WAS NOT AVAILABLE; SO THE FLC TRIED TO CONTACT COMPANY ON THE LCL FREQ. NO ANSWER; SO WE DECIDED WE COULD HAVE MADE AN ERROR FOR THE ARPT WE SERVE IN ST LUCIA. UPON FURTHER INVESTIGATION; WE LEARNED THAT SLU WAS NOT HEWANORRA; BUT WAS CASTRIES. ANOTHER FLT PLAN WAS FILED WITH TWR AND THE FLT WAS CONTINUED TO CASTRIES AND THEN SAN JUAN WITHOUT INCIDENT. THE ERROR (HEWANORRA AS OUR CORRECT DEST) WAS MADE BECAUSE DAYS PRIOR TO THE FLT IN PREPARATION; I ASKED TWO PLTS WHERE THE IATA CODE SLU WAS AND BOTH OF THEIR REPLIES WERE ST LUCIA. I LOOKED IN THE CHARTS SECTION OF OUR COMPANY'S COMMERCIAL APCH PLATES AND FOUND ST LUCIA (HEWANORRA). MY FO CAME TO THE SAME CONCLUSION PRIOR TO THE FLT. ICAO CODES WOULD HAVE BEEN CHKED PRIOR IF THERE WOULD HAVE BEEN A REASON PRIOR TO THE FLT TO QUESTION HEWANORRA AS OTHER THAN THE CORRECT DEST. SUPPLEMENTAL INFO FROM ACN 524024: WE HAD AN UNSCHEDULED FLT FROM DOMINICA (FOM) TO SAINT LUCIA (SLU). IT WAS THE SECOND SEGMENT OF THE DAY AND WE WERE REPOSITIONING THE AIRPLANE EMPTY TO SAINT LUCIA FROM DOMINICA. DURING OUR FLT; IT WAS REQUESTED AND GIVEN CLRNC DIRECT TO BNF VOR; AFTERWARDS WE'VE CLRED FOR THE VOR DMG RWY 10 TO HEWANORRA ARPT. WE CHECKED OUR APCH PLTS AND WE BRIEFED THE APCH. AFTER LNDG; THE TWR GUIDED US TO THE GATE WHERE WE REALIZED AFTER THE LACK OF SERVICES THAT WE WERE AT THE WRONG ARPT. EVEN THOUGH WE WERE NEVER OUR OF CONTROL OF THE AIRPLANE OR OUR SIT AWARENESS; THE COMPANY RELEASED WAS FOR SAINT LUCIA 'CASTRIES' ARPT AND ON THE COMMERCIAL FLT MANUAL; IT IS LOCATED UNDER SECTION C FOR CASTRIES. THE ARPT WE LANDED AT WAS UNDER SECTION S. THE MISTAKE WAS MADE BECAUSE WE OPENED THE COMMERCIAL CHART AND FOUND NO OTHER ARPT UNDER SAINT LUCIA IN SECTION S AND NEITHER OF US DOUBLE CHECKED THE IATA CODES WITH THE ICAO LUCIA BEFORE; THE MISTAKE WAS MADE. AFTER THE REALIZATION OF THE MISTAKE WE ASKED AND RECEIVED ANOTHER CLRNC TO SLU AND CONTINUED TO OUR DEST WE WERE NEVER WITHOUT COMMUNICATIONS AND WE ACTUALLY WERE CLRED TO LAND TO SAINT LUCIA; BUT THE COMPANY NEVER INTENDED FOR US TO GO THERE.