LTSS PLTDEV BTWN CPR JET AND UNKNOWN ACFT WHILE IN DSCNT CAUGHT UP AND PASSED AN UNKNOWN ACFT AT THE SAME ALT. CTR CTLR MISCOM AN INAPPROPRIATE COMMAND TO THE FLC TO BEGIN DSCNT AFTER THE ACFT WAS ALREADY IN DSCNT FROM PREVIOUS DSCNT CLRNC TO 17000 FT AND ADDING AN EXPECT TO CROSS RESTR OF 11000 FT. THE CPR JET WAS NON MODE C. THE FLC; EXPECTING THE XING RESTR; DSNDED THROUGH 17000 FT WITHOUT A CLRNC.

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CTLR STATES; 'ABC DSND TO 17000 FT; LAS ALTIMETER 30.30.' I ACCEPT THIS 17000 FT ALT ASSIGNMENT. (2 THINGS MUST NOTE: 1) WE ARE OPERATING WITHOUT MODE C; 2) I AM LISTENING AND RELISTENING TO THE COPY OF THE ATC TAPE WE GOT UNDER THE FOI ACT; AS I WRITE THIS.) NOW WE ARE DSNDING FROM AROUND FL284 TO 17000 FT. DURING THIS DSCNT I GO OFF FREQ TO GET ATIS. I AM JUST COMING BACK FROM ATIS WHEN I SEE THE PF DSNDING (OR ABOUT TO DSND) THROUGH THE ALT SET ON THE ALT ALERTER. I POINT TO THE ALT ALERTER ALT AND HE CONFIDENTLY WAVES ME OFF AND SAYS THAT WE ARE TO CROSS CROWE INTXN AT 11000 FT. WHAT I DIDN'T KNOW THEN; BUT HEARD ON THE TAPE LATER; WAS THAT AS WE WERE DSNDING THROUGH ABOUT FL200 HE HEARD THE CTLR SAY 'ABC; BEGIN DSCNT AND EXPECT TO CROSS CROWE AT 11000 FT.' THIS CALL WAS NOT ACKNOWLEDGED BECAUSE OF OTHER IMMEDIATE XMISSIONS FROM OTHER ACFT. THEN HE HEARD 'ABC; START YOUR DSCNT (SPOKEN EMPHATICALLY) AND...UH...WE NEED YOU TO BE...EXPECT TO CROSS CROW AT 11000 FT...EXPECT THAT.' I JUST CAME BACK ON FREQ IN TIME TO SAY; 'OK; WE ARE DSNDING AND EXPECT CROW AT 11000 FT.' SHORTLY AFTER THIS; THE DEV OCCURRED. THIS CAUSED THE ATC ALARM TO SOUND WHEN WE CAUGHT UP FROM BEHIND AND PASSED ANOTHER IFR ACFT WITHIN THE LATERAL LIMITS WHILE AT HIS ALT.