TWIN TURBOPROP CREW INBOUND TO DEN ARPT BELIEVED THEY WERE CLRED TO 9000 FT. THEY CONTACTED APCH CTL DSNDING THROUGH 10400 FT WHEN THEY RECEIVED A TCASII TA. APCH CTL INSTRUCTED THE FLT TO MAINTAIN 11000 FT.

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AT APPROX XA35 LCL; WE (ACR X) WERE AT 13000 FT; HDG 300 DEGS; AT 190 KIAS; ABOUT 20 NM SW OF DEN. APCH CTL 120.35 TOLD US TO TURN R TO 345 DEGS; DSND AND MAINTAIN 9000 FT; AND CONTACT DEN APCH 123.85. 123.85 WAS VERY BUSY AND I WAITED TO GET IN; WHILE WE WERE DSNDING. OUR TCASII ALERTED US OF 'TFC.' I IMMEDIATELY CALLED APCH AND SAID 'ACR X 10600 FT FOR 9000 FT.' 123.85 SAID 'MAINTAIN 11000 FT.' BY NOW WE WERE AT 10400 FT AND I RPTED '190400 FT FOR 11000 FT.' WE CAME TOO CLOSE TO AN ACFT DEPARTING DEN. WE CLBED TO 11000 FT AND LATER LANDED SAFELY AT DEN. THE FACT THAT BOTH CTLRS WERE BUSY AND THAT I WAS UNABLE TO GET IN AND CHK ON BEFORE PASSING 11000 FT CONTRIBUTED. IT IS POSSIBLE THAT I WAS IN ERROR. BUT I STRONGLY BELIEVE THAT I WAS TOLD 9000 FT BY 120.35 BEFORE THE HDOF. PERHAPS; BECAUSE OF THE CONGESTION; THE CTLRS WERE UNABLE TO CONFIRM MY READBACK. IN ANY EVENT; I BELIEVE THAT THIS WAS HUMAN ERROR. MINE POSSIBLY; OR POSSIBLY THE CTLR'S. THAT WOULD BE SOLVED BY THE TAPES. OUR TCASII PROVED VERY USEFUL TODAY.