Narrative:

Aircraft #1 C560 was level at FL330 needing to land at biv; just outside my airspace. C650; aircraft #2; was level at FL320 landing at rst just outside my airspace. I was busy with close to 20+ aircraft on my scope and I was at the position by myself. I was attempting to descend aircraft #2 to FL310; stepping #2 down around traffic. Aircraft #1 took the clearance and I missed the readback. Traffic was issued before they passed. Aircraft #1 said that he had the second aircraft on TCAS. He waited until they passed and then started his descent. Separation was lost when they were tail-to-tail. Things that could have prevented this error: 1) use of aircraft types when dealing with cpr's. 2) listening closely to readbacks; lowering of volume on control room floor. There was a shift change going on with 3 supervisors at the desk and several controllers roaming throughout the area. The supervisors were at the desk and none were on the floor. The bae hi sector always gets busy during this time of day and the need for a d-side should be closely monitored. I'm sure that aircraft #1's readback was drowned out by all the backgnd noise but then I failed to confirm the readback from the pilot. This error occurred 25 mins before the end of my shift. There was WX in the area throughout the morning but was gone by this time. Finally; another contributing factor is the FAA's desire to increase our time on position. Our area leads the building in 2+ hours on position grievances filing as many as 17 in 1 shift this summer. We spend many useless hours sitting on d-sides with no traffic; diminishing our skills and when it gets busy it gets harder to be as on top or 'ahead of the problem' than it used to be. This is my first deal in 15 yrs; so I'm sure this was a contributing factor.

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Original NASA ASRS Text

Title: ZAU CTLR EXPERIENCED OPERROR AT FL320 AS ACFT WITH SIMILAR CALL SIGN ACCEPTS DSCNT CLRNC INTENDED FOR ANOTHER ACFT AND CTLR MISSED INCORRECT READBACK.

Narrative: ACFT #1 C560 WAS LEVEL AT FL330 NEEDING TO LAND AT BIV; JUST OUTSIDE MY AIRSPACE. C650; ACFT #2; WAS LEVEL AT FL320 LNDG AT RST JUST OUTSIDE MY AIRSPACE. I WAS BUSY WITH CLOSE TO 20+ ACFT ON MY SCOPE AND I WAS AT THE POS BY MYSELF. I WAS ATTEMPTING TO DSND ACFT #2 TO FL310; STEPPING #2 DOWN AROUND TFC. ACFT #1 TOOK THE CLRNC AND I MISSED THE READBACK. TFC WAS ISSUED BEFORE THEY PASSED. ACFT #1 SAID THAT HE HAD THE SECOND ACFT ON TCAS. HE WAITED UNTIL THEY PASSED AND THEN STARTED HIS DSCNT. SEPARATION WAS LOST WHEN THEY WERE TAIL-TO-TAIL. THINGS THAT COULD HAVE PREVENTED THIS ERROR: 1) USE OF ACFT TYPES WHEN DEALING WITH CPR'S. 2) LISTENING CLOSELY TO READBACKS; LOWERING OF VOLUME ON CTL ROOM FLOOR. THERE WAS A SHIFT CHANGE GOING ON WITH 3 SUPVRS AT THE DESK AND SEVERAL CTLRS ROAMING THROUGHOUT THE AREA. THE SUPVRS WERE AT THE DESK AND NONE WERE ON THE FLOOR. THE BAE HI SECTOR ALWAYS GETS BUSY DURING THIS TIME OF DAY AND THE NEED FOR A D-SIDE SHOULD BE CLOSELY MONITORED. I'M SURE THAT ACFT #1'S READBACK WAS DROWNED OUT BY ALL THE BACKGND NOISE BUT THEN I FAILED TO CONFIRM THE READBACK FROM THE PLT. THIS ERROR OCCURRED 25 MINS BEFORE THE END OF MY SHIFT. THERE WAS WX IN THE AREA THROUGHOUT THE MORNING BUT WAS GONE BY THIS TIME. FINALLY; ANOTHER CONTRIBUTING FACTOR IS THE FAA'S DESIRE TO INCREASE OUR TIME ON POS. OUR AREA LEADS THE BUILDING IN 2+ HRS ON POS GRIEVANCES FILING AS MANY AS 17 IN 1 SHIFT THIS SUMMER. WE SPEND MANY USELESS HRS SITTING ON D-SIDES WITH NO TFC; DIMINISHING OUR SKILLS AND WHEN IT GETS BUSY IT GETS HARDER TO BE AS ON TOP OR 'AHEAD OF THE PROB' THAN IT USED TO BE. THIS IS MY FIRST DEAL IN 15 YRS; SO I'M SURE THIS WAS A CONTRIBUTING FACTOR.

Data retrieved from NASA's ASRS site as of January 2009 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.