Narrative:

I was assigned to the tallahassee low radar associate position. WX was impacting the area and WX deviations were occurring. The radar controller was trying to work an light transport to a higher altitude (presently at 16000') in an mdt inbound to tallahassee requested to remain as high as possible (FL220). The radar controller cleared the mdt to FL180. Due to low altimeters, 29.85, FL180 was unusable. After spotting opp direction traffic at 17000' the pilot of the light transport asked for a VFR climb, requesting FL220. The radar controller cleared the light transport to climb VFR through FL180, climb and maintain FL220. The light transport was slightly ahead of the mdt same direction. After marking this clearance on the flight progress strips, I questioned the radar controller about the VFR climb through FL180? He paused and stated to separate the aircraft. A very busy and WX impacted sector caused the pilots to request unusual things. In an attempt to accommodate the pilots, and the light transport's request for VFR climb, the radar controller failed to see the mdt catching up from behind. His thinking was that the climb was clean and free of conflicts.

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Original NASA ASRS Text

Title: AN ACFT CLIMBING FROM 16000' TO FL220 WAS OVERTAKEN BY AN ACFT AT FL180 AS THE CLIMBING ACFT PASSED THROUGH FL180.

Narrative: I WAS ASSIGNED TO THE TALLAHASSEE LOW RADAR ASSOCIATE POS. WX WAS IMPACTING THE AREA AND WX DEVS WERE OCCURRING. THE RADAR CTLR WAS TRYING TO WORK AN LTT TO A HIGHER ALT (PRESENTLY AT 16000') IN AN MDT INBND TO TALLAHASSEE REQUESTED TO REMAIN AS HIGH AS POSSIBLE (FL220). THE RADAR CTLR CLRED THE MDT TO FL180. DUE TO LOW ALTIMETERS, 29.85, FL180 WAS UNUSABLE. AFTER SPOTTING OPP DIRECTION TFC AT 17000' THE PLT OF THE LTT ASKED FOR A VFR CLB, REQUESTING FL220. THE RADAR CTLR CLRED THE LTT TO CLB VFR THROUGH FL180, CLB AND MAINTAIN FL220. THE LTT WAS SLIGHTLY AHEAD OF THE MDT SAME DIRECTION. AFTER MARKING THIS CLRNC ON THE FLT PROGRESS STRIPS, I QUESTIONED THE RADAR CTLR ABOUT THE VFR CLB THROUGH FL180? HE PAUSED AND STATED TO SEPARATE THE ACFT. A VERY BUSY AND WX IMPACTED SECTOR CAUSED THE PLTS TO REQUEST UNUSUAL THINGS. IN AN ATTEMPT TO ACCOMMODATE THE PLTS, AND THE LTT'S REQUEST FOR VFR CLB, THE RADAR CTLR FAILED TO SEE THE MDT CATCHING UP FROM BEHIND. HIS THINKING WAS THAT THE CLB WAS CLEAN AND FREE OF CONFLICTS.

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.