Narrative:

Took a handoff on northbound aircraft X over aldan at 9000 ft and I was already working an aircraft level at 10000 ft. Rdu tower and ZDC have an LOA that states propellers cross aldan at 8000 ft unless coordinated. The air carrier B was a propeller and had descended to 10000 ft to stop him above the 9000 ft traffic (aircraft X). After working out some other business in the sector I saw that rdu had accepted the handoff and air carrier B needed to be switched. I gave him a frequency change to rdu and at the last min noticed he was a propeller and cleared him to 8000 ft with the 9000 ft traffic ahead on about 5-8 mi. I realized the mistake and called rdu to tell them the situation and to stop the air carrier B at 10000 ft or turn him. With the lack of immediate concern or action rdu could not keep separation from being lost.

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Original NASA ASRS Text

Title: ATC CLRS AN ACFT TO DSND THROUGH AN OCCUPIED ALT. SEPARATION IS LOST.

Narrative: TOOK A HDOF ON NBOUND ACFT X OVER ALDAN AT 9000 FT AND I WAS ALREADY WORKING AN ACFT LEVEL AT 10000 FT. RDU TWR AND ZDC HAVE AN LOA THAT STATES PROPS CROSS ALDAN AT 8000 FT UNLESS COORDINATED. THE ACR B WAS A PROP AND HAD DSNDED TO 10000 FT TO STOP HIM ABOVE THE 9000 FT TFC (ACFT X). AFTER WORKING OUT SOME OTHER BUSINESS IN THE SECTOR I SAW THAT RDU HAD ACCEPTED THE HDOF AND ACR B NEEDED TO BE SWITCHED. I GAVE HIM A FREQ CHANGE TO RDU AND AT THE LAST MIN NOTICED HE WAS A PROP AND CLRED HIM TO 8000 FT WITH THE 9000 FT TFC AHEAD ON ABOUT 5-8 MI. I REALIZED THE MISTAKE AND CALLED RDU TO TELL THEM THE SIT AND TO STOP THE ACR B AT 10000 FT OR TURN HIM. WITH THE LACK OF IMMEDIATE CONCERN OR ACTION RDU COULD NOT KEEP SEPARATION FROM BEING LOST.

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.