Narrative:

Air carrier X (DC9) was outbound from stl eastbound on the blues 1 departure at FL270 requesting higher (stopped for sbound traffic at FL280). Light transport (Y) (DA10) was wbound at FL270 requesting higher after departing an airport in the center (ZID)/sector adjacent to my airspace. Light transport (Y) had traffic immediately overhead at FL280 wbound and requesting FL260 through FL280 to conduct air refueling. This aircraft (KC135) was not a factor with air carrier X. When air carrier X cleared the sbound FL280 traffic, I issued a clearance to climb and maintain FL290 and expedite the climb. Exactly 1 and 1/2 mins later, I cleared light transport (Y) to turn left heading 240 (approximately 30 degrees) in order to move him south of the air refuel airspace (and KC135 at FL280). As soon as light transport (Y) started to read back the clearance, I realized that air carrier X had not copied the climb clearance and would be in immediate conflict with light transport (Y). When light transport (Y) completed the readback, I canceled that clearance and issued an immediate right turn heading 290 degrees and issued air carrier X a right turn heading 180 degrees. There was insufficient time to prevent loss of separation to 4 mi. Contributing factors: there was WX to the east/southeast of the general location of these 3 aircraft causing numerous deviations by other aircraft. The frequency was congested and I was having to repeat many xmissions. I feel many pilots were not properly monitoring the frequency before transmitting. I feel the direct cause was the failure of air carrier X to receive and execute the clearance to climb, but the primary problem was my failure to insure the clearance was received and executed prior to issuing turn clearance to light transport (Y). My mind told me one thing, but this in fact was not the fact (that air carrier X had climbed).

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Original NASA ASRS Text

Title: ARTCC RADAR CTLR TURNED AN ACR DC9 AND CLBED HIM FROM SAME ALT AS A FALCON AND TO CLR A MIL TANKER WHO WAS REQUESTING A BLOCK ALT THAT BOTH THE ACR AND FALCON WERE IN. THE ACR DID NOT HEAR HIS CLB CLRNC AND THE FALCON WAS TURNED SO AS TO BECOME TFC FOR THE ACR. THE CTLR INTERVENED, BUT NOT BEFORE SEPARATION WAS LOST.

Narrative: ACR X (DC9) WAS OUTBOUND FROM STL EBOUND ON THE BLUES 1 DEP AT FL270 REQUESTING HIGHER (STOPPED FOR SBOUND TFC AT FL280). LTT (Y) (DA10) WAS WBOUND AT FL270 REQUESTING HIGHER AFTER DEPARTING AN ARPT IN THE CTR (ZID)/SECTOR ADJACENT TO MY AIRSPACE. LTT (Y) HAD TFC IMMEDIATELY OVERHEAD AT FL280 WBOUND AND REQUESTING FL260 THROUGH FL280 TO CONDUCT AIR REFUELING. THIS ACFT (KC135) WAS NOT A FACTOR WITH ACR X. WHEN ACR X CLRED THE SBOUND FL280 TFC, I ISSUED A CLRNC TO CLB AND MAINTAIN FL290 AND EXPEDITE THE CLB. EXACTLY 1 AND 1/2 MINS LATER, I CLRED LTT (Y) TO TURN L HDG 240 (APPROX 30 DEGS) IN ORDER TO MOVE HIM S OF THE AIR REFUEL AIRSPACE (AND KC135 AT FL280). AS SOON AS LTT (Y) STARTED TO READ BACK THE CLRNC, I REALIZED THAT ACR X HAD NOT COPIED THE CLB CLRNC AND WOULD BE IN IMMEDIATE CONFLICT WITH LTT (Y). WHEN LTT (Y) COMPLETED THE READBACK, I CANCELED THAT CLRNC AND ISSUED AN IMMEDIATE R TURN HDG 290 DEGS AND ISSUED ACR X A R TURN HDG 180 DEGS. THERE WAS INSUFFICIENT TIME TO PREVENT LOSS OF SEPARATION TO 4 MI. CONTRIBUTING FACTORS: THERE WAS WX TO THE E/SE OF THE GENERAL LOCATION OF THESE 3 ACFT CAUSING NUMEROUS DEVS BY OTHER ACFT. THE FREQ WAS CONGESTED AND I WAS HAVING TO REPEAT MANY XMISSIONS. I FEEL MANY PLTS WERE NOT PROPERLY MONITORING THE FREQ BEFORE XMITTING. I FEEL THE DIRECT CAUSE WAS THE FAILURE OF ACR X TO RECEIVE AND EXECUTE THE CLRNC TO CLB, BUT THE PRIMARY PROB WAS MY FAILURE TO INSURE THE CLRNC WAS RECEIVED AND EXECUTED PRIOR TO ISSUING TURN CLRNC TO LTT (Y). MY MIND TOLD ME ONE THING, BUT THIS IN FACT WAS NOT THE FACT (THAT ACR X HAD CLBED).

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.