LACK OF CLARIFICATION OF CLRNC BY ZAU CAUSES CONFLICT BTWN DSNDING CARJ AND F100 AFTER FREQ CHANGE TO C90.

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ON THE PMM 4 ARR INTO ORD; WE WERE CLRED TO HOLD AT THE PIVOT INTXN; EFC XB10. CTLR (CTR) THEN TOLD US TO MAINTAIN 250 KTS APPROX 10-15 MI FROM PIVOT INTXN. CAPT TOLD CTLR WE WOULD NEED TO HOLD AT 210 KTS. CTLR SAID THAT HE WAS TRYING TO GET US IN; BUT WE MAY HAVE TO DO 1 TURN (IN HOLDING). APPROX 5 MI; CAPT ASKED CTLR TO CONFIRM THAT HE WANTED US TO HOLD AT 250 KTS. CTLR SAID TO MAINTAIN 250 KTS. JUST BEFORE PIVOT INTXN (APPROX 1-2 MI); CTR TOLD US TO DSND TO 10000 FT AND CONTACT APCH. THE CAPT CHKED IN WITH APCH AS I ENTERED HOLDING. AT APPROX 10400 FT; STILL IN THE TURN; WE RECEIVED A CLB RA. I CONTINUED THE R-HAND TURN AND IMMEDIATELY COMPLIED WITH THE RA SEEING THE OTHER ACFT AT OUR 12 O'CLOCK POS AND TRAVELING R TO L. THE CAPT INFORMED APCH THAT WE WERE COMPLYING WITH THE RA. THE APCH CTLR THEN ISSUED A R TURN AND TOLD US TO MAINTAIN 11000 FT. WE WERE THEN VECTORED FOR A NORMAL APCH AND LNDG TO ORD. FROM THE CONVERSATION BTWN THE CAPT AND THE APCH CTLR IMMEDIATELY FOLLOWING THE RA; IT IS MY OPINION THAT THE APCH CTLR WAS NOT EXPECTING US TO ENTER THE HOLD. THAT WAS OUR LAST CLRNC GIVEN FROM CTR BEFORE THE HDOF. SUPPLEMENTAL INFO FROM ACN 539970: UPON CLRING THE CONFLICT; APCH ASKED US IF WE HAD BEEN HOLDING. WE RESPONDED YES. AFTER COORDINATING WITH OUR COMPANY ATC MGR; IT BECAME APPARENT THAT THE CTR CTLR HAD MEANT TO CANCEL OUR HOLD CLRNC AND THAT ORD APCH EXPECTED US TO CONTINUE ON THE ARR. BECAUSE NO CANCELLATION WAS EVER GIVEN; WE HAD COMPLIED WITH OUR LAST CLRNC. SUPPLEMENTAL INFO FROM ACN 539996: AFTER HOLDING AT PIVOT AT 10000 FT; WE WERE ON A 300 DEG HDG WHEN TCASII RA DIRECTED US TO DSND. ANOTHER AFT WAS DSNDING TOWARDS US FROM THE L. TOLD ATC THAT WE WERE DEVIATING; THEN WHEN CLR OF CONFLICT; WE CLBED BACK TO 10000 FT. SUPPLEMENTAL INFO FROM ACN 540181: I SAW AND MENTIONED TO THE CAPT ABOUT THE ACFT WHEN HE HAD ALREADY DSNDED TO 400 FT ABOVE OUR ALT. WE INFORMED ATC OF THE RA AND THAT WE WERE RETURNING TO 10000 FT. THEY FAILED TO ANSWER AFTER REPEATED CALLS FOR ALMOST A MIN. BY THE TIME THEY ANSWERED OUR CALL; THE OTHER ACFT SHOWED BACK LEVEL AT 11000 FT. NO MENTION OF WHAT WAS HAPPENING WAS MADE ON THE RADIO BY ATC.