ACR X TCASII TA RA WITH SMA Y IN TFC PATTERN MULTIPLE RWY OP PARALLEL RWYS. SEE AND AVOID CONCEPT.

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THE INCIDENT OCCURRED DURING THE LAST PHASE OF A CIRCLING APCH TO CHICAGO MIDWAY. ACR X WAS A REGULARLY SCHEDULED FLT WHICH ENDED IN A CLRNC FOR AN ILS RWY 31C; CIRCLE TO LAND RWY 22L. ALL WENT WELL DURING THE APCH TO 31C WITH THE MINOR EXCEPTION OF THE CIRCLE TO 22L BEING UNEXPECTED DUE TO PREVIOUS ATIS STATING THE WINDS WERE CALM. THE APCH CTLR CHANGED THE WIND WHEN QUERIED TO SOMETHING LIKE 250/12; HE SAID THEIR WIND INDICATOR WAS INTERMITTENTLY INOP. AS THE CAPT COMPLETED THE BASE TO FINAL TURN ABOUT A MI OR 2 OUT FROM 22L; WE GOT A TCASII TA FOR AN ACFT AT OUR 2 O'CLOCK AND ABOUT 1 TO 2 MI. I CONTINUED SCANNING FOR TFC AND PICKED UP SEVERAL LIGHT AIRPLANES IN THE PATTERN. A FEW SECONDS LATER; THE TA WENT TO AN RA WITH A COMMAND OF 'CLB; CLB; CLB.' I IMMEDIATELY XCHKED THE SPECIFIC TARGET; SAW WHAT I THOUGHT WAS A SMALL PLANE TURNING WHAT APPEARED TO BE A R BASE TO FINAL FOR RWY 22R. SIMULTANEOUS TO THESE OCCURRENCES; TWR CALLED TO ADVISE US OF THAT TFC; AN SMA Y; WHICH WAS ; IN FACT; TURNING IN FOR 22R. HAVING ADVISED THE CAPT THAT I HAD THE TFC AND TO CONTINUE WHILE I KEPT AN EYE ON HIM; WE COMPLETED THE APCH AND LNDG. ONCE IN OPS; I CALLED THE TWR TO INQUIRE AS TO THE CLOSENESS OF SUCH SIMULTANEOUS VISUAL APCHS TO PARALLEL RUNWAYS; AND WAS INFORMED THAT THIS TYPE OF OP WAS STANDARD PRACTICE THERE TO RWYS 22L AND 22R. EVEN THOUGH THESE 2 RWYS ARE ONLY 920 FT APART; AND TWR CTLR; WITH THE SUPVR'S LISTENING AND NOT CONTRADICTING CONCURRENCE; STATED THAT THEY HAD TO DO THIS WITH THESE 2 RWYS AS THE OTHER 3 - 13L AND 13R - WERE ONLY 775 FT APART.