FOREIGN ARPT HAS ALT RESTR EVEN WHEN ACFT ARE CLRED FOR A VISUAL APCH. RPTR FO KNEW OF THE RESTR; BUT WAS DISTRACTED BY OTHER COCKPIT DUTIES AND DIDN'T NOTICE THAT THE CAPT; PF; HAD SET THE ALT ALERT ABOVE THEIR ALT THINKING CLRED FOR A VISUAL GAVE HIM THE PREROGATIVE TO DSND.

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DURING APCH INTO ARUBA WE WERE CLRED TO DSND TO 4000 FT (FL40). DURING DSCNT APPROX 12 NM N; WE CALLED FIELD IN SIGHT; WE WERE CLRED FOR A VISUAL APCH; CALL L BASE. WE CONTINUED DSCNT BELOW 4000 FT; TWR CALLED US AS WE WERE DSNDING THROUGH APPROX 3000 FT AND ADVISED US WE WERE NOT CLRED TO DSND WHEN GIVEN A VISUAL APCH CLRNC. WE WERE THEN TOLD TO CONTINUE DSCNT AND LAND. WE DID. UNEVENTFUL. I'VE FLOWN INTO ARUBA MANY TIMES. I WAS AWARE OF THEIR ATC RULES FOR VISUAL APCHS. I SHOULD HAVE BACKED UP THE PF. THIS IS ONE OF 2 PLACES IN THE WORLD I'VE FLOWN WHERE THIS RULE EXISTS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR FO IDENTED THE ACFT AS B757-200. THE DUTCH ISLES; ARUBA AND ST MAARTEN; HAVE A PROC THAT REQUIRES ARRIVING ACFT TO MAINTAIN ALT UNTIL CLRED TO DSND. WHEN THE RPTR FLC WAS CLRED FOR THE VISUAL APCH; THE RPTR FO WAS INVOLVED IN COCKPIT DUTIES SUCH AS CHKLISTS; ETC; AND DIDN'T NOTICED THAT THE CAPT HAD MOVED THE ALT ALERT KNOB TO A HIGHER ALT (TO ELIMINATE ANNOYING ALT ALERT WARNINGS) AND; THINKING THAT WITH A VISUAL APCH CLRNC HE COULD DSND AT HIS DISCRETION. CONSEQUENTLY HE DSNDED BELOW 4000 FT ASSIGNED AND THE APCH CTLR QUESTIONED THEM ON THEIR ALT. THE CTLRS THERE REFER TO THE ASSIGNED ALT IN THE ARPT AREA AS 'CIRCUIT ALT.' ARUBA DOES NOT HAVE A CERTIFIED RADAR ENVIRONMENT; BUT IT WAS EVIDENT THAT THEY HAD RADAR OPERATING. RPTR FAULTS HIMSELF SOMEWHAT BECAUSE HE KNEW OF THE PROCS AND DIDN'T MONITOR THE CAPT CLOSE ENOUGH AND THE CAPT WAS NEW TO THE AREA. WHEN ASKED HOW THE RPTR KNEW OF THAT PROC RESTR AT ARUBA HE SAID FROM EXPERIENCE; THOUGH HE THINKS IT IS DEPICTED ON HIS COMPANY'S ARPT PAGE.