ARTCC radar controller failed to maintain vertical separation between tower descending aircraft.

Attributes
ACN	144821
Time
Date	199005
Day	Sun
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : ctf
State Reference	SC
Altitude	msl bound lower : 10000 msl bound upper : 10000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : ztl
Operator	general aviation : corporate
Make Model Name	Medium Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 14
ASRS Report	144821
Person 2
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	conflict : airborne less severe
Independent Detector	other flight crewa
Resolutory Action	controller : issued new clearance other
Consequence	faa : investigated
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Working continued radar position during busy rush to 2 separate airports. Frequency congestion restr area along route. Mdt en route to clt over ctf descending to 10000'. Medium large transport en route clt over ctf at 16000'. Cleared mdt to descend to 10000' per LOA. Started his descent, then cleared medium large transport to descend to 10000'. Should have been 11000', thought I said 11000'. Busy with providing entrail for raleigh, nc, aircraft. Noticed mdt not descending at 10700'. Asked him to hurry. Told medium large transport to maintain 12000'. Medium large transport was at 13600'. Mdt reported reaching 10000'. Reclred medium large transport to 10000' again thinking 11000'. Entered 11000' in data block of medium large transport. At ctf medium large transport reported descending to 10000' and he asked the altitude of aircraft beneath him. Told medium large transport his clearance was to maintain 11000'. I was told by medium large transport he was given 10000' and climbing to 11000'. Called traffic to mdt. Conflict alert goes off briefly. I switched both aircraft to receiving approach control. Reported situation to my supervisor as possible pilot deviation. The 'error detection' computer did not detect a loss of appropriate sep.

Original NASA ASRS Text

Title: ARTCC RADAR CTLR FAILED TO MAINTAIN VERTICAL SEPARATION BETWEEN TWR DESCENDING ACFT.

Narrative: WORKING CONTINUED RADAR POS DURING BUSY RUSH TO 2 SEPARATE ARPTS. FREQ CONGESTION RESTR AREA ALONG RTE. MDT ENRTE TO CLT OVER CTF DSNDING TO 10000'. MLG ENRTE CLT OVER CTF AT 16000'. CLRED MDT TO DSND TO 10000' PER LOA. STARTED HIS DSNT, THEN CLRED MLG TO DSND TO 10000'. SHOULD HAVE BEEN 11000', THOUGHT I SAID 11000'. BUSY WITH PROVIDING ENTRAIL FOR RALEIGH, NC, ACFT. NOTICED MDT NOT DSNDING AT 10700'. ASKED HIM TO HURRY. TOLD MLG TO MAINTAIN 12000'. MLG WAS AT 13600'. MDT RPTED REACHING 10000'. RECLRED MLG TO 10000' AGAIN THINKING 11000'. ENTERED 11000' IN DATA BLOCK OF MLG. AT CTF MLG RPTED DSNDING TO 10000' AND HE ASKED THE ALT OF ACFT BENEATH HIM. TOLD MLG HIS CLRNC WAS TO MAINTAIN 11000'. I WAS TOLD BY MLG HE WAS GIVEN 10000' AND CLBING TO 11000'. CALLED TFC TO MDT. CONFLICT ALERT GOES OFF BRIEFLY. I SWITCHED BOTH ACFT TO RECEIVING APCH CTL. RPTED SITUATION TO MY SUPVR AS POSSIBLE PLT DEV. THE 'ERROR DETECTION' COMPUTER DID NOT DETECT A LOSS OF APPROPRIATE SEP.

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.