Narrative:

Air carrier X was descended as per normal operating procedure. After seeing potential traffic, I tried to resolve by reclring air carrier X to another altitude, but mistakenly stated wrong altitude. Aircraft passed with 2.3 mi lateral and 600 ft vertical. Supplemental information from acn 202172: air carrier X was inadvertently descended to FL240 from FL270 by radar controller. I was assisting controller with manual duties when I noticed air carrier X was getting close to loss of separation with cpr Y. Basically separation was lost (600 ft/2.3 NM). This was attained after air carrier X was issued a climb by the controller and had simultaneously climbed due to a TCASII advisory. The TCASII advised air carrier X to 'climb' when the cpr Y was at FL262 descending to FL250 and was approximately 10 NM from cpr Y. Cpr Y was issued descent, but in keeping with his previous frequency presence and sluggish response, he never took the clearance. The thing to be noticed was that TCASII did, in fact, aid in the physical separation of the 2 aircraft. However, I believe that the TCASII chose the wrong solution and should've 'descended' air carrier X from FL262 to FL250 as per ATC instructions and this would've provided a more effective means of aircraft separation. Surely, if the controller would've noticed the incident. While air carrier X were still descending at FL262 and 10 NM from cpr Y, he would've had enough time to prevent an error.

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Original NASA ASRS Text

Title: ACR X TCASII RA CLB HAD LTSS FROM CPR Y. EVASIVE ACTION TAKEN. SYS ERROR.

Narrative: ACR X WAS DSNDED AS PER NORMAL OPERATING PROC. AFTER SEEING POTENTIAL TFC, I TRIED TO RESOLVE BY RECLRING ACR X TO ANOTHER ALT, BUT MISTAKENLY STATED WRONG ALT. ACFT PASSED WITH 2.3 MI LATERAL AND 600 FT VERT. SUPPLEMENTAL INFO FROM ACN 202172: ACR X WAS INADVERTENTLY DSNDED TO FL240 FROM FL270 BY RADAR CTLR. I WAS ASSISTING CTLR WITH MANUAL DUTIES WHEN I NOTICED ACR X WAS GETTING CLOSE TO LOSS OF SEPARATION WITH CPR Y. BASICALLY SEPARATION WAS LOST (600 FT/2.3 NM). THIS WAS ATTAINED AFTER ACR X WAS ISSUED A CLB BY THE CTLR AND HAD SIMULTANEOUSLY CLBED DUE TO A TCASII ADVISORY. THE TCASII ADVISED ACR X TO 'CLB' WHEN THE CPR Y WAS AT FL262 DSNDING TO FL250 AND WAS APPROX 10 NM FROM CPR Y. CPR Y WAS ISSUED DSCNT, BUT IN KEEPING WITH HIS PREVIOUS FREQ PRESENCE AND SLUGGISH RESPONSE, HE NEVER TOOK THE CLRNC. THE THING TO BE NOTICED WAS THAT TCASII DID, IN FACT, AID IN THE PHYSICAL SEPARATION OF THE 2 ACFT. HOWEVER, I BELIEVE THAT THE TCASII CHOSE THE WRONG SOLUTION AND SHOULD'VE 'DSNDED' ACR X FROM FL262 TO FL250 AS PER ATC INSTRUCTIONS AND THIS WOULD'VE PROVIDED A MORE EFFECTIVE MEANS OF ACFT SEPARATION. SURELY, IF THE CTLR WOULD'VE NOTICED THE INCIDENT. WHILE ACR X WERE STILL DSNDING AT FL262 AND 10 NM FROM CPR Y, HE WOULD'VE HAD ENOUGH TIME TO PREVENT AN ERROR.

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.