ACR X CLB TO OCCUPIED ALT HAD LTSS FROM SMA Y. SYS ERROR.

Narrative

I WAS WORKING A COMBINED SECTOR WITHOUT A HDOF CTLR. WORKLOAD WAS MODERATE TO BUSY. ACR X CONTACTED ME LEVEL AT 7000; TURNING TO JOIN V64 EBOUND. I ALREADY HAD SMA Y ON THE AIRWAY EBOUND AT 11000. KNOWING ACR X COULD NOT OUT CLB SMA Y (HE WAS IN TRAIL TO THE SMA); I HAD PLANNED TO STOP ACR X AT 10000 AND GO UNDERNEATH SMA Y PRIOR TO CLBING ACR X TO 14000. WHEN I ISSUED THE ALT INSTEAD OF ISSUING 10000 AS INTENDED I ISSUED 11000 WHICH THE PLT READ BACK. THINKING ACR X WAS CLBING TO 10000; I ISSUED TFC TO ACR X AS 'TFC; 12 O'CLOCK; 6 MI; EBOUND; SMA Y AT 11000' WHICH THE PLT ROGERED FOR. SHORTLY THEREAFTER I TURNED SMA Y NEBOUND OFF THE AIRWAY TO ALLOW ACR X TO CONTINUE TO CLB. WHILE WAITING FOR SMA Y TO TURN OUT OF THE WAY CONFLICT ALERT WAS ACTIVATED AND I SAW ACR X AT 11000 AND IN CLOSE PROX TO SMA Y. I IMMEDIATELY ISSUED TFC TO ACR X WHICH THE PLT RPTED IN SIGHT. I INSTRUCTED ACR X TO MAINTAIN VISUAL SEPARATION FROM THE SMA Y AND TO CONTINUE CLB. UPON QUESTIONING THE PLT OF ACR X HE STATED HE WAS ISSUED A CLB TO 11000 WHICH WAS CONFUSING TO ME AS I THOUGHT I HAD ISSUED A CLB TO 10000. A SUBSEQUENT REVIEW OF THE TAPES SHOWED THAT I HAD IN FACT ISSUED A CLB TO 11000. I FEEL THAT THE CAUSAL FACTORS IN THIS ERROR WERE WORKLOAD AT THE TIME AND NOT REALLY LISTENING TO WHAT I ACTUALLY SAID OR THE PLT READBACK. I ALREADY HAD SMA Y AT 11000 AND ANOTHER ACFT CLBING TO 11000 AND IN THINKING 10000 I INADVERTENTLY ISSUED 11000. A STUPID MISTAKE! IN THE FUTURE I PLAN TO CALL FOR HELP SOONER AND TO STRIVE TO IMPROVE MY LISTENING SKILLS TO AVOID THIS SORT OF INCIDENT.