Air carrier X had less than standard separation from air carrier Y system error.

Attributes
ACN	208184
Time
Date	199204
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : bna
State Reference	TN
Altitude	msl bound lower : 21000 msl bound upper : 22000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zme
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
ASRS Report	208184
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	conflict : airborne less severe 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 other
Consequence	faa : investigated
Miss Distance	horizontal : 22800 vertical : 900
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

I was working 460 at ZME on the morning of apr/tue/92. The morning rush had just started and I was working approximately 11 aircraft. Air carrier X was inbound to bna from over cha at FL280 pilot's discretion to FL240 leaving FL280. This aircraft is required by LOA with ZTL to be at FL240 crossing the boundary. Air carrier was inbound to bna from over tys at FL230 pilot's discretion to FL200. The ZTL LOA requires aircraft over tys to be at or below FL230 descending FL200. My first plan was to descend air carrier X to FL190 and get him under air carrier Y. I descended air carrier X to FL190 and turned him to a 360 heading. Then I decided this wasn't going to work so I stopped air carrier X at FL210 above air carrier Y who I thought was at FL200, but was actually at FL230 with pilot's discretion to FL200. I then descended air carrier Y to 17000 and a few seconds later to 14000. Approximately 51 seconds later, I saw air carrier Y leaving FL227 and realized I had a problem. I stopped air carrier Y at FL220 and turned air carrier X 30 degrees left. The closest they came to each other was 3.8 and 900 ft. Air carrier Y never reported leaving FL230 and made a comment about having the traffic on TCASII when I stopped him at FL220.

Original NASA ASRS Text

Title: ACR X HAD LTSS FROM ACR Y SYS ERROR.

Narrative: I WAS WORKING 460 AT ZME ON THE MORNING OF APR/TUE/92. THE MORNING RUSH HAD JUST STARTED AND I WAS WORKING APPROX 11 ACFT. ACR X WAS INBOUND TO BNA FROM OVER CHA AT FL280 PLT'S DISCRETION TO FL240 LEAVING FL280. THIS ACFT IS REQUIRED BY LOA WITH ZTL TO BE AT FL240 XING THE BOUNDARY. ACR WAS INBOUND TO BNA FROM OVER TYS AT FL230 PLT'S DISCRETION TO FL200. THE ZTL LOA REQUIRES ACFT OVER TYS TO BE AT OR BELOW FL230 DSNDING FL200. MY FIRST PLAN WAS TO DSND ACR X TO FL190 AND GET HIM UNDER ACR Y. I DSNDED ACR X TO FL190 AND TURNED HIM TO A 360 HDG. THEN I DECIDED THIS WASN'T GOING TO WORK SO I STOPPED ACR X AT FL210 ABOVE ACR Y WHO I THOUGHT WAS AT FL200, BUT WAS ACTUALLY AT FL230 WITH PLT'S DISCRETION TO FL200. I THEN DSNDED ACR Y TO 17000 AND A FEW SECONDS LATER TO 14000. APPROX 51 SECONDS LATER, I SAW ACR Y LEAVING FL227 AND REALIZED I HAD A PROBLEM. I STOPPED ACR Y AT FL220 AND TURNED ACR X 30 DEGS L. THE CLOSEST THEY CAME TO EACH OTHER WAS 3.8 AND 900 FT. ACR Y NEVER RPTED LEAVING FL230 AND MADE A COMMENT ABOUT HAVING THE TFC ON TCASII WHEN I STOPPED HIM AT FL220.

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.