Narrative:

We were using an unusual traffic pattern at the time due to WX. Aircraft normally on a downwind leg at 6000' were assigned to 4000'. I was watching the aircraft on the downwind (being worked by an adjacent controller) well aware of its altitude of 4000'. I had a departure come off of a crossing runway assigned to maintain 3000' by the tower. It was clear in my mind that the departure should remain at 3000' for sep from the downwind traffic. However, when I responded to the departure's initial callup, I transposed the altitude I was looking at on the downwind traffic (being 4000') to the altitude I assigned to the departure, placing the aircraft in conflict. I was not aware of the problem until the controller next to me and I both noticed the departure climbing through 3400'. At the same time the pilot of the departure asked me about the altitude of the traffic passing overhead. I told the pilot that the overhead traffic was maintaining 4000' and that he had been assigned 3000'. The pilot then informed me that I had assigned him 4000'. I subsequently asked the supervisor to pull the tape for verification. The tape revealed my error. Evasive action was not required. Contributing factors were adverse WX, unusual traffic flow, and my inattn to what I actually said and listening to the pilot's readback for errors. Supplemental information from acn 97652: there was air carrier Y above us and on a collision course with us. The copilot lowered the nose and descended back down to 3300'. Our highest altitude was 3500'.

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Original NASA ASRS Text

Title: LESS THAN STANDARD SEPARATION BETWEEN 2 ACR ACFT.

Narrative: WE WERE USING AN UNUSUAL TFC PATTERN AT THE TIME DUE TO WX. ACFT NORMALLY ON A DOWNWIND LEG AT 6000' WERE ASSIGNED TO 4000'. I WAS WATCHING THE ACFT ON THE DOWNWIND (BEING WORKED BY AN ADJACENT CTLR) WELL AWARE OF ITS ALT OF 4000'. I HAD A DEP COME OFF OF A XING RWY ASSIGNED TO MAINTAIN 3000' BY THE TWR. IT WAS CLEAR IN MY MIND THAT THE DEP SHOULD REMAIN AT 3000' FOR SEP FROM THE DOWNWIND TFC. HOWEVER, WHEN I RESPONDED TO THE DEP'S INITIAL CALLUP, I TRANSPOSED THE ALT I WAS LOOKING AT ON THE DOWNWIND TFC (BEING 4000') TO THE ALT I ASSIGNED TO THE DEP, PLACING THE ACFT IN CONFLICT. I WAS NOT AWARE OF THE PROB UNTIL THE CTLR NEXT TO ME AND I BOTH NOTICED THE DEP CLBING THROUGH 3400'. AT THE SAME TIME THE PLT OF THE DEP ASKED ME ABOUT THE ALT OF THE TFC PASSING OVERHEAD. I TOLD THE PLT THAT THE OVERHEAD TFC WAS MAINTAINING 4000' AND THAT HE HAD BEEN ASSIGNED 3000'. THE PLT THEN INFORMED ME THAT I HAD ASSIGNED HIM 4000'. I SUBSEQUENTLY ASKED THE SUPVR TO PULL THE TAPE FOR VERIFICATION. THE TAPE REVEALED MY ERROR. EVASIVE ACTION WAS NOT REQUIRED. CONTRIBUTING FACTORS WERE ADVERSE WX, UNUSUAL TFC FLOW, AND MY INATTN TO WHAT I ACTUALLY SAID AND LISTENING TO THE PLT'S READBACK FOR ERRORS. SUPPLEMENTAL INFO FROM ACN 97652: THERE WAS ACR Y ABOVE US AND ON A COLLISION COURSE WITH US. THE COPLT LOWERED THE NOSE AND DSNDED BACK DOWN TO 3300'. OUR HIGHEST ALT WAS 3500'.

Data retrieved from NASA's ASRS site as of August 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.