Air carrier was descended to analt occupied by another aircraft.

Attributes
ACN	120430
Time
Date	198908
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : orm
State Reference	FL
Altitude	msl bound lower : 20000 msl bound upper : 21000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zjx
Operator	general aviation : personal
Make Model Name	Small Transport, Low Wing, 2 Recip Eng
Flight Phase	cruise 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 : handoff position
Qualification	controller : radar
Experience	controller radar : 1
ASRS Report	120430
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 25
ASRS Report	120289
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 : 18450 vertical : 300
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error Intra Facility Coordination Failure

Narrative:

Small transport X was southbound to land melbourne with a clearance to cross 25 mi so of omn VORTAC at 13000'. Air carrier Y was southbound to land mlo. I thought that small transport X was still assigned FL200 since he wa still showing FL199 in the data block. The radar controller gave air carrier Y FL200 which I was checking with the d-side what altitude small transport X wa assigned. It was 13000', he was just staying up. I did not hear the radar controller assign air carrier FL200, and when I looked back at the scope air carrier Y was descending. I don't remember for sure on this point, but I think the radar controller pointed at air carrier Y and said he had given him FL210. I typed FL210 into air carrier Y's data block. The radar controller began to turn small transport X w-erly and air carrier Y e-erly to facilitate their dscnts. We then looked at other situations. The C/a activated as air carrier Y descended through FL210 a small transport X wa still at FL200. The radar controller turned both aircraft farther, but they got below the minimum requirements. Supplemental information from acn 120289: corrective action: let the radar controller enter all altitude changes into the computer, unless the change is pointed out to the radar controller.

Original NASA ASRS Text

Title: ACR WAS DESCENDED TO ANALT OCCUPIED BY ANOTHER ACFT.

Narrative: SMT X WAS SBND TO LAND MELBOURNE WITH A CLRNC TO CROSS 25 MI SO OF OMN VORTAC AT 13000'. ACR Y WAS SBND TO LAND MLO. I THOUGHT THAT SMT X WAS STILL ASSIGNED FL200 SINCE HE WA STILL SHOWING FL199 IN THE DATA BLOCK. THE RADAR CTLR GAVE ACR Y FL200 WHICH I WAS CHKING WITH THE D-SIDE WHAT ALT SMT X WA ASSIGNED. IT WAS 13000', HE WAS JUST STAYING UP. I DID NOT HEAR THE RADAR CTLR ASSIGN ACR FL200, AND WHEN I LOOKED BACK AT THE SCOPE ACR Y WAS DSNDING. I DON'T REMEMBER FOR SURE ON THIS POINT, BUT I THINK THE RADAR CTLR POINTED AT ACR Y AND SAID HE HAD GIVEN HIM FL210. I TYPED FL210 INTO ACR Y'S DATA BLOCK. THE RADAR CTLR BEGAN TO TURN SMT X W-ERLY AND ACR Y E-ERLY TO FACILITATE THEIR DSCNTS. WE THEN LOOKED AT OTHER SITUATIONS. THE C/A ACTIVATED AS ACR Y DSNDED THROUGH FL210 A SMT X WA STILL AT FL200. THE RADAR CTLR TURNED BOTH ACFT FARTHER, BUT THEY GOT BELOW THE MINIMUM REQUIREMENTS. SUPPLEMENTAL INFO FROM ACN 120289: CORRECTIVE ACTION: LET THE RADAR CTLR ENTER ALL ALT CHANGES INTO THE COMPUTER, UNLESS THE CHANGE IS POINTED OUT TO THE RADAR CTLR.

Data retrieved from NASA's ASRS site as of August 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.