T75 CTLR ISSUES C650 PLT 6000 FT AND IS READ BACK AND ACKNOWLEDGED BY T75 AS 7000 FT; AND COMES INTO CONFLICT WITH AN ACR AT 7000 FT.

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WE TOOK OFF FROM SUS; RECEIVING RADAR VECTORS AND CLB ASSIGNMENTS FROM STL DEP CTL. CLB WAS ISSUED TO 5000 FT MSL. LEVEL AT 5000 FT; CAPT (PNF); FO IS THE PF. ALL RADIO XMISSIONS ARE FROM THE CAPT. CTLR ISSUED A CLB TO 7000 FT. (THIS IS WHAT WE HEARD.) CALL WAS ANSWERED; AND 7000 FT SELECTED IN THE ALT PRESELECT. CALL WAS VERIFIED BY THE FO. CLBING THROUGH 6000 FT; CTLR ISSUED A TA AS 'OPPOSITE DIRECTION; LEVEL 7000 FT.' I IMMEDIATELY MADE VISUAL CONTACT; AND REALIZED THE IMPENDING CONFLICT; AND ASKED THE CTLR TO VERIFY 7000 FT. CTLR IMMEDIATELY SAID 'NEGATIVE; 6000 FT.' I ASSUMED CTL OF THE ACFT AND RETURNED TO 6000 FT. (I ESTIMATE ACFT WAS AT 6600 FT MSL WHEN I ASSUMED CTL.) CTLR ADVISED US TO CONTACT TRACON WHEN WE LANDED. I SPENT 15 MINS ON THE PHONE WITH TRACON SUPVR; AS WE DISCUSSED THE IMPORTANCE OF VIGILANCE IN ALT ASSIGNMENTS. SUPVR SAID THE TAPES SAID AS FOLLOWS: ATC -- 'ACFT X; CLB; MAINTAIN 6000 FT.' CAPT -- 'CLBING 7000 FT; TA.' ATC -- 'AFFIRMATIVE.' (I READ BACK THE ASSIGNMENT INCORRECTLY AND SUPVR VERIFIED IT.) I WILL STRIVE IN THE FUTURE TO PAY THE CLOSEST SCRUTINY TO ATC ASSIGNMENTS AND INSURE MY READBACKS OF ALT ASSIGNMENTS ARE CLRLY STATED. IT IS MY UNDERSTANDING THAT THE OTHER ACFT WAS AN ACR JET; WHICH RECEIVED AN RA TO OUR ALTDEV. VMC PREVAILED; AND THE EPISODE WAS HANDLED EXPEDITIOUSLY AND SMOOTHLY. IT WAS THE CLASSIC 'READ BACK THE WRONG ALT AND AFFIRMED' SCENARIO. I AM COMMITTING MYSELF TO PAY CLOSER ATTN TO ATC INSTRUCTIONS; AND IF THE ASSIGNMENT IS NOT HEARD PERFECTLY CLR; TO ASK FOR A VERIFICATION. THE ATC SUPVR WAS VERY PROFESSIONAL; AND UNDERSTOOD THE MAGNITUDE OF THE PROB WE PLT AND CTLRS DEAL WITH ON A DAILY BASIS. AS SUPVR STATED; ALL WE CAN DO IS MAINTAIN VIGILANCE; AND DO OUR JOBS AS BEST WE CAN; WITH SAFETY OUR #1 GOAL. AS YOU CAN SEE; THIS SYS IS NOT FLAWLESS; YET 99% OF THE TIME; IT WORKED PERFECTLY EVEN IN BUSY AIRSPACE. I HAVE LEARNED A LOT FROM THIS EPISODE.