Air carrier was descended to an occupied altitude resulting in less than standard separation.

Attributes
ACN	139951
Time
Date	199003
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : tay
State Reference	FL
Altitude	msl bound lower : 27000 msl bound upper : 28000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zjx
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	descent other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 20
ASRS Report	139951
Person 2
Affiliation	government : faa
Function	controller : non radar
Qualification	controller : radar
Experience	controller radar : 2
ASRS Report	139829
Events
Anomaly	non adherence : published procedure non adherence : required legal separation
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	controller : issued new clearance
Consequence	Other
Miss Distance	horizontal : 11500 vertical : 600
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Air carrier X came on frequency north of tay at FL280 requesting lower due to moderate turbulence, obtained a release from R49 to descend air carrier X. Air carrier Y was handed off and switched to R49. Issued descent to air carrier X and did not observe air carrier Y as traffic (data blocks overlapped) after override call from R49 turned air carrier X to heading 270 degree. Not realizing air carrier Y had to be turned by R49, issued new turn to air carrier X and altitude clearance. When manual dig called for release on air carrier X R49 did not advise of air carrier Y as traffic and released air carrier X for descent. Supplemental information from acn 139829. While working the radar associate (manual) position, I observed the adjacent controller descend an aircraft through one he had just handed to the sector I was working. The error was discovered almost immediately. Both aircraft were issued immediate turns, but the proximity of the aircraft when turns were issued prevented the controllers from maintaining standard sep. The only factor I see contributing to the error was simple human oversight.

Original NASA ASRS Text

Title: ACR WAS DESCENDED TO AN OCCUPIED ALT RESULTING IN LESS THAN STANDARD SEPARATION.

Narrative: ACR X CAME ON FREQ N OF TAY AT FL280 REQUESTING LOWER DUE TO MODERATE TURB, OBTAINED A RELEASE FROM R49 TO DSND ACR X. ACR Y WAS HANDED OFF AND SWITCHED TO R49. ISSUED DSCNT TO ACR X AND DID NOT OBSERVE ACR Y AS TFC (DATA BLOCKS OVERLAPPED) AFTER OVERRIDE CALL FROM R49 TURNED ACR X TO HDG 270 DEG. NOT REALIZING ACR Y HAD TO BE TURNED BY R49, ISSUED NEW TURN TO ACR X AND ALT CLRNC. WHEN MANUAL DIG CALLED FOR RELEASE ON ACR X R49 DID NOT ADVISE OF ACR Y AS TFC AND RELEASED ACR X FOR DSCNT. SUPPLEMENTAL INFO FROM ACN 139829. WHILE WORKING THE RADAR ASSOCIATE (MANUAL) POS, I OBSERVED THE ADJACENT CTLR DSND AN ACFT THROUGH ONE HE HAD JUST HANDED TO THE SECTOR I WAS WORKING. THE ERROR WAS DISCOVERED ALMOST IMMEDIATELY. BOTH ACFT WERE ISSUED IMMEDIATE TURNS, BUT THE PROX OF THE ACFT WHEN TURNS WERE ISSUED PREVENTED THE CTLRS FROM MAINTAINING STANDARD SEP. THE ONLY FACTOR I SEE CONTRIBUTING TO THE ERROR WAS SIMPLE HUMAN OVERSIGHT.

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.