C208 ATX PLT HAS AN NMAC WITH A TRI-ISLANDER ATX XING IN FRONT OF HIM. ACFT X WAS ON FINAL FOR SJU. ACFT Y WAS ON A BASE LEG FOR ISLA GRANDE ARPT. RADAR WAS OTS.

Narrative

THE FOLLOWING EVENT TOOK PLACE OCT/XA/97 AT AB22. THE LOCATION OF THIS INCIDENT WAS ESTIMATED TO BE 5 NM S OF ISLA GRANDE ARPT; OR ABOUT 1 NM S OF PATTY (SJ) LOM AT 1500 FT MSL. I WAS PIC OF ACFT ON FINAL FOR SJU RWY 10. THE OTHER ACFT INVOLVED WAS A BRITTEN NORMAN TRI- ISLANDER. FLT WAS CONDUCTED UNDER VFR RULES AND CONDITIONS; AND THE ALTIMETER SETTING WAS 29.99 INCHES OF MERCURY. THE FLT CONDITIONS AT THE TIME OF THE INCIDENT WERE CAVU. I WAS ON A 080 DEG HDG; BTWN THE 2 LOCS OF SJU IN A DIRECT COURSE FOR THE ARPT. THE FLT WAS ON ITS FINAL LEG RETURNING FROM PONCE TO SJU; AND AFTER LEVELING OFF AT 1500 FT I PROCEEDED TO COMPLETE THE BEFORE LNDG CHKLIST. AFTER COMPLETING THE BEFORE LNDG CHKLIST I LOOKED OUTSIDE MY L WINDOW TO MY 9 O'CLOCK POS TO BEGIN AN OUTSIDE SCAN FROM L TO R. TO MY SURPRISE; WHEN LOOKING AT MY 11 O'CLOCK POS; THERE WAS A BRITTEN NORMAN TRI- ISLANDER TURNING TOWARD ISLA GRANDE ARPT IN WHAT LOOKED LIKE A R BASE FOR RWY 9 AT ISLA GRANDE ARPT. I HAVE ESTIMATED THE SEPARATION BTWN BOTH ACFT TO BE 200 FT HORIZ SEPARATION AND 100 FT VERT SEPARATION. THE ACFT HAD ALREADY CROSSED MY FLT PATH FROM MY R TO MY L. AT THIS TIME NO EVASIVE ACTION WAS NECESSARY. NO INJURIES OR DAMAGE RESULTED FROM THIS INCIDENT. MY PAX; SEATED TO MY R; TOLD ME THAT HE HAD SEEN THE OTHER ACFT AND EVEN WHEN HE THOUGHT THAT IT WAS CLOSER THAN NORMAL DID NOT SAY ANYTHING BECAUSE HE BELIEVED THAT I HAD THE ACFT IN SIGHT. I NEVER HEARD THE OTHER ACFT ON TWR FREQ. FACTORS THAT INFLUENCED THIS INCIDENT ARE THAT BOTH ACFT WERE ON DIFFERENT FREQS; I WAS TALKING TO SJU TWR AND THE OTHER ACFT WAS TALKING TO SJU APCH; THE SJU ASR WAS DOWN FOR MAINT AFTER A COUPLE OF FAILURES DURING THE PAST FEW MONTHS. ALSO; THE FACT THAT MY PAX DID NOT ADVISE WHEN HE SAW THE OTHER ACFT AND THOUGHT IT WAS A LITTLE CLOSE TO US. I SHOULD ALSO MENTION THE TIME I SPEND (ABOUT 30 SECONDS) LOOKING INSIDE THE COCKPIT TO COMPLETE A CHKLIST WITHIN 5 MI OF THE DEST ARPT. I ELECTED NOT TO ADVISE THE TWR OF THE INCIDENT UNTIL I WAS SAFELY ON THE GND; WHERE I CALLED THE TWR TO INFORM THE INCIDENT. AN INVESTIGATION IS UNDER WAY TO FIND OUT WHERE THE SYS FAILED SO THAT ANOTHER ENCOUNTER LIKE THIS ONE CAN BE PREVENTED.