RPT OF LOSS OF SEPARATION BTWN AN ACR B747 AT FL330 AND MIL C21 DSNDING TO FL290. THE C21 WAS NOT AT OR BELOW FL310 BEFORE LATERAL SEPARATION OF 5 MI WAS LOST WITH THE B747.

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ACR X WAS NE AT FL330 AND MIL Y EBOUND DIRECT RIC. I HAD 20 MI LATERAL SEPARATION. BOTH ACFT AT FL330. I PLACED A 5 MI HOOP ON ACR X AND DSNDED MIL Y TO FL310 FROM FL330 WITH NO XING RESTR WHICH AT A NORMAL DSCNT RATE SEPARATION WOULD HAVE BEEN MAINTAINED. TFC IN THE SECTOR WAS BUILDING. ON MY SCAN; I NOTICED MIL Y MODE C FL315 DSNDING WITH 8 MI LATERAL SEPARATION. I DID NOT CALL TFC TO EITHER ACFT UNTIL CONFLICT ALERT ACTIVATED ON MY RADAR WITH MIL Y AT FL317 DSNDING 6 MI IN FRONT OF ACR X WHO WAS OVERTAKING. I ASKED MIL Y TO VERIFY LEVEL AT FL310. HE REPLIED HE WAS DSNDING TO FL310. I ISSUED FURTHER DSCNT TO FL290 AND TOLD MIL Y I NEED A RPT OUT OF FL310. NOW HE SAID WE'RE DSNDING TO FL310 AND TO VERIFY ASSIGNED ALT; WHICH I DID; AND TOLD HIM TO RPT LEAVING FL310. TFC WAS CALLED TO ACR X 12 O'CLOCK; 6 MI; LEAR DSNDING SAME DIRECTION. THE INVESTIGATION REVEALED MIL Y DSNDED TO FL313; THEN CLBED TO FL317; THEN DSNDED WHEN QUESTIONED BY ME. SEPARATION WAS LOST WITH MIL Y 4.2 MI IN FRONT OF ACR X AT FL330 AND MIL Y AT FL315 TO FL317. HAD I GIVEN A RESTR TO BE LEVEL; SEPARATION WOULD NOT HAVE BEEN LOST. HAD MIL Y DSNDED TO FL310 AT STANDARD RATE OF DSCNT; WHICH IS NOT 1000 FPM FOR A LEAR; OR WOULD NOT HAVE CLBED FROM FL313 TO FL317 AND BACK TO FL310; SEPARATION WOULD HAVE BEEN MAINTAINED. IF ALL PLTS WHEN GIVEN A DSCNT AND MAINTAIN CLRNC WOULD START DOWN AND AT THE STANDARD RATE AS PUBLISHED IN THE AIM SOME OF THESE PROBS WOULD NOT OCCUR. ACR X WAS TCASII EQUIPPED BUT NEVER MENTIONED AN RA WHICH HAD HE; THINGS WOULD HAVE BEEN WORSE. HE HAD TFC ABOVE HIM AT FL350.