SMA Y HAD LTSS FROM ACR X MAKING VISUAL APCH. SYS ERROR.

Narrative

THE PROBLEM BEGAN WHEN ACR X WAS CLRED FOR A VISUAL APCH APPROX 15 MI W AND INSTRUCTED TO 'CONTACT TWR XING THE RIVER' WHICH WAS ABOUT 10 W OF THE ARPT. SMA Y WAS ON AN IFR FLT PLAN ALSO INBOUND BUT FROM THE NW ON A CONVERGING COURSE WITH ACR X. SMA Y WAS DSNDING TO 3000; STILL INBOUND ON AN AIRWAY WHICH PUT HIM ALMOST STRAIGHT-IN TO THE ARR RWY. THE PLT OF SMA Y VIVIDLY EXPRESSED HIS APPRECIATION FOR BEING ASSIGNED THE STRAIGHT-IN RWY. WHEN I SAW THAT SMA Y; WHO WAS APPROX EQUIDISTANT FROM THE RWY WITH ACR X; WAS NOT REDUCING AS I HAD EXPECTED; I SAW THAT I WOULD NEED TO VECTOR SMA Y OFF OF HIS STRAIGHT-IN FOR SEQUENCE. I ASSIGNED THE VECTOR AND THE PLT QUESTIONED IT. I THEN ASSIGNED ANOTHER VECTOR AND TOLD THE PLT TO TURN NOW. BY THIS TIME; ACR X WAS CERTAINLY NOT GOING TO MISS SMA Y BY 3 MI; BUT ACR X WAS STILL 1500 FT ABOVE SMA Y. I ASSIGNED ACR X AN ALT 1000 FT ABOVE SMA Y; BUT ACR X DID NOT RESPOND (HE HAD CONTACTED TWR WHILE XING THE RIVER). IF I WOULD HAVE DONE ONE OF 2 THINGS; THE LOSS OF SEPARATION WOULD NOT HAVE OCCURRED. 1) NOT CLR AND SWITCH ACR X UNTIL THE POTENTIAL CONFLICT WAS RESOLVED. 2) REDUCE OR VECTOR SMA Y EARLIER.