Narrative:

I was in the last hours of my shift working a complex and busy sector (sector 27). Military use of R5802 (a/B/C) constricted my available altitudes. ZOB did not provide in trail space between 2 phl arrs. Aircraft X (a citation) descending to FL250; and aircraft Y (a B737) level at FL190. An arrival to hgr (propeller aircraft) at FL180 above the R5802 active space was traffic for both phl arrs. I descended aircraft Y to 16000 ft; and when I saw the aircraft leave 17000 ft; I descended aircraft X to 17000 ft so that both would be below the hgr arrival prior to har VOR. Then I attended to other duties in the scenario and began speed control and vectoring to establish in trail between aircraft X and aircraft Y phl arrs. About 10 mi west of har VOR; I got a radar hit indicating aircraft Y at altitude 17400 ft descending. I immediately reclred aircraft X to maintain FL180; then went back to get an altitude report from aircraft Y who reported level at 16000 ft. This was probably a 'mode C swap' -- a common and confusing problem. Once I had the report; I intended to reclr aircraft X to 17000 ft; but said 16000 ft by mistake. I caught the error as aircraft X left 16800 ft descending and had him maintain 17000 ft. No TCASII event; as far as I know.

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Original NASA ASRS Text

Title: ZNY CTLR EXPERIENCED OPERROR AT 16000 FT WHILE DSNDING 2 ACFT TO LOWER ALTS.

Narrative: I WAS IN THE LAST HRS OF MY SHIFT WORKING A COMPLEX AND BUSY SECTOR (SECTOR 27). MIL USE OF R5802 (A/B/C) CONSTRICTED MY AVAILABLE ALTS. ZOB DID NOT PROVIDE IN TRAIL SPACE BTWN 2 PHL ARRS. ACFT X (A CITATION) DSNDING TO FL250; AND ACFT Y (A B737) LEVEL AT FL190. AN ARR TO HGR (PROP ACFT) AT FL180 ABOVE THE R5802 ACTIVE SPACE WAS TFC FOR BOTH PHL ARRS. I DSNDED ACFT Y TO 16000 FT; AND WHEN I SAW THE ACFT LEAVE 17000 FT; I DSNDED ACFT X TO 17000 FT SO THAT BOTH WOULD BE BELOW THE HGR ARR PRIOR TO HAR VOR. THEN I ATTENDED TO OTHER DUTIES IN THE SCENARIO AND BEGAN SPD CTL AND VECTORING TO ESTABLISH IN TRAIL BTWN ACFT X AND ACFT Y PHL ARRS. ABOUT 10 MI W OF HAR VOR; I GOT A RADAR HIT INDICATING ACFT Y AT ALT 17400 FT DSNDING. I IMMEDIATELY RECLRED ACFT X TO MAINTAIN FL180; THEN WENT BACK TO GET AN ALT RPT FROM ACFT Y WHO RPTED LEVEL AT 16000 FT. THIS WAS PROBABLY A 'MODE C SWAP' -- A COMMON AND CONFUSING PROB. ONCE I HAD THE RPT; I INTENDED TO RECLR ACFT X TO 17000 FT; BUT SAID 16000 FT BY MISTAKE. I CAUGHT THE ERROR AS ACFT X LEFT 16800 FT DSNDING AND HAD HIM MAINTAIN 17000 FT. NO TCASII EVENT; AS FAR AS I KNOW.

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.