Narrative:

Air carrier X was northeast at FL330 and military Y eastbound direct ric. I had 20 mi lateral separation. Both aircraft at FL330. I placed a 5 mi hoop on air carrier X and descended military Y to FL310 from FL330 with no crossing restr which at a normal descent rate separation would have been maintained. Traffic in the sector was building. On my scan, I noticed military Y mode C FL315 descending with 8 mi lateral separation. I did not call traffic to either aircraft until conflict alert activated on my radar with military Y at FL317 descending 6 mi in front of air carrier X who was overtaking. I asked military Y to verify level at FL310. He replied he was descending to FL310. I issued further descent to FL290 and told military Y I need a report out of FL310. Now he said we're descending to FL310 and to verify assigned altitude, which I did, and told him to report leaving FL310. Traffic was called to air carrier X 12 O'clock, 6 mi, lear descending same direction. The investigation revealed military Y descended to FL313, then climbed to FL317, then descended when questioned by me. Separation was lost with military Y 4.2 mi in front of air carrier X at FL330 and military Y at FL315 to FL317. Had I given a restr to be level, separation would not have been lost. Had military Y descended to FL310 at standard rate of descent, which is not 1000 FPM for a lear, or would not have climbed from FL313 to FL317 and back to FL310, separation would have been maintained. If all pilots when given a descent and maintain clearance would start down and at the standard rate as published in the aim some of these problems would not occur. Air carrier X was TCASII equipped but never mentioned an RA which had he, things would have been worse. He had traffic above him at FL350.

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Original NASA ASRS Text

Title: 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.

Narrative: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.