DURING A VISUAL APCH TO RWY 8 A B757-200 FLT CREW PERFORMS A GAR WHEN TFC SEPARATION FROM OTHER TFC ON A VISUAL TO RWY 10 APPEARS TO BE TOO CLOSE TO SJU.

Narrative

APCHING SJU OUR FLT WAS CLRED FOR THE ILS RWY 10 TO THE LAGOON VISUAL APCH; CLRED TO LAND ON RWY 8. WE WERE ADVISED OF TFC S OF THE ARPT ON R BASE TO RWY 10 ON A VISUAL APCH. I DO NOT REMEMBER IF WE RPTED THE OTHER TFC IN SIGHT ON INITIAL ADVISORY. HOWEVER; WE DID HAVE THE OTHER ACFT IN SIGHT AT ALL TIMES. AS WE APCHED THE ARPT I ADVISED THE FO (PF) THAT THE TFC APPEARED TO BE CONVERGING AND IF IT BECAME NECESSARY TO GO AROUND TO AVOID TFC; TO OFFSET TO THE N AWAY FROM THE TFC. AT SOMEWHERE AROUND 500 FT THE TFC WAS IN MY OPINION TOO CLOSE TO CONTINUE THE APCH. TCASII GAVE A TFC ALERT AT THE SAME TIME AND WE EXECUTED A GAR. RETURN TO THE ARPT WAS NORMAL WITH ABOUT A 10 MIN DELAY. AFTER LNDG THE TWR QUERIED US AS TO THE REASON FOR THE GAR. I REPLIED 'INADEQUATE SEPARATION; TCASII ALERT AND 2 AIRPLANES OCCUPYING THE SAME AIRSPACE AT THE SAME TIME.' THE TWR ASKED US TO CALL AFTER PARKING. WHEN I TALKED TO THE TWR CAB; THEY WANTED TO KNOW THE REASON FOR THE GAR; AS I CITED INADEQUATE SEPARATION. I REPLIED IT MAY HAVE BEEN WITHIN THEIR REQUIREMENTS; BUT I FELT IT WAS TOO CLOSE FOR US AND WE ELECTED TO GO AROUND. HE ASKED IF WE HAD THE OTHER TFC IN SIGHT WHEN ADVISED. I SAID WE DID; BUT AS THE TFC CONVERGED; IT DIDN'T LOOK SAFE TO CONTINUE; SO WE WENT AROUND. THE TWR ASKED IF WE HAD DONE THIS TYPE OF APCH BEFORE. I STATED I HAD AND HAVE EVEN BEEN THE ACFT ON THE S SIDE TO RWY 10. THE TWR IMPLIED THEY WERE HAPPY WITH THE ANSWERS. MY SAFETY CONCERNS WITH THESE APCHS ARE AS FOLLOWS: AT SJU; THE BRIDGE VISUAL TO RWY 10 AND THE LAGOON VISUAL TO RWY 8 ARE CONVERGING APCHS REQUIRING LOW ALT MANEUVERING BELOW 500 FT. ACFT APCHING FROM THE S ON THE BRIDGE VISUAL ARE REQUIRED TO MAKE A 90 DEG R TURN TO FINAL WHILE ACFT ON THE LAGOON VISUAL ARE REQUIRED TO MAKE A L TURN ABOUT 20 DEGS. FINAL APCH COURSES OF THESE 2 RWY INTERSECT APPROX 3000 FT FROM THE APCH END OF THE RWYS. THE POSSIBILITY OF AN ACFT TURNING TO RWY 10 OVERSHOOTING FINAL IS HIGH. THE MANEUVERING ALSO PUTS BOTH ACFT BELLY TO BELLY IN SUCH A POS THAT PLTS WILL LOSE VISUAL CONTACT WITH THE OTHER AT LOW ALT. I RECOMMEND THAT SEPARATION BE GIVEN TO ACFT TO ENSURE THAT APCHS ARE STAGGERED ENOUGH TO ENSURE AN OVERSHOOT IS NOT CATASTROPHIC. SUPPLEMENTAL INFO FROM ACN 634216: THIS PRESENTED ITSELF VISUALLY BY CONSTANT BEARING AND DECREASING RANGE TO TFC (A TURBOPROP). SEVERAL PAX THANKED US AFTER LNDG FOR MOVING AWAY FROM TFC THAT APPEARED TO BE VERY CLOSE IN THEIR ESTIMATION.