Light transport X had less than standard separation from air carrier Y. System error.

Attributes
ACN	130917
Time
Date	198912
Day	Tue
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : hyk
State Reference	KY
Altitude	msl bound lower : 35000 msl bound upper : 35000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zid
Make Model Name	Light Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent other
Route In Use	enroute : on vectors enroute : direct
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	cruise other
Route In Use	enroute : direct enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller non radar : 3 controller radar : 3
ASRS Report	130917
Person 2
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 : 18000 vertical : 1200
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

I was working the somerset super high sector at ind ARTCC. I owned FL350 and above. Light transport X departed cmh en route to cha. Called on frequency leveling at FL370. Air carrier Y, en route from atl to dtw at FL350. Traffic was dying down. I only had 8 aircraft on frequency. I knew light transport X landed at cha, and was approximately 175 mi from the airport. Light transport X asked for lower. I descended him to FL350, the lowest altitude in my stratum. Air carrier Y was basically head-on and 15 mi away. I started to point out light transport X to the high altitude sector below mine, and was going to request lower. Something didn't feel right, but I couldn't put my finger on what was wrong. It dawned on me that light transport X and air carrier X were traffic, and I turned both aircraft. I realized my mistake too late and wound up with less than standard separation. I've been trying to determine why I failed to see they were traffic, but I haven't come up with an answer. I just flight out missed the traffic.

Original NASA ASRS Text

Title: LTT X HAD LESS THAN STANDARD SEPARATION FROM ACR Y. SYSTEM ERROR.

Narrative: I WAS WORKING THE SOMERSET SUPER HIGH SECTOR AT IND ARTCC. I OWNED FL350 AND ABOVE. LTT X DEPARTED CMH ENRTE TO CHA. CALLED ON FREQ LEVELING AT FL370. ACR Y, ENRTE FROM ATL TO DTW AT FL350. TFC WAS DYING DOWN. I ONLY HAD 8 ACFT ON FREQ. I KNEW LTT X LANDED AT CHA, AND WAS APPROX 175 MI FROM THE ARPT. LTT X ASKED FOR LOWER. I DSNDED HIM TO FL350, THE LOWEST ALT IN MY STRATUM. ACR Y WAS BASICALLY HEAD-ON AND 15 MI AWAY. I STARTED TO POINT OUT LTT X TO THE HIGH ALT SECTOR BELOW MINE, AND WAS GOING TO REQUEST LOWER. SOMETHING DIDN'T FEEL RIGHT, BUT I COULDN'T PUT MY FINGER ON WHAT WAS WRONG. IT DAWNED ON ME THAT LTT X AND ACR X WERE TFC, AND I TURNED BOTH ACFT. I REALIZED MY MISTAKE TOO LATE AND WOUND UP WITH LTSS. I'VE BEEN TRYING TO DETERMINE WHY I FAILED TO SEE THEY WERE TFC, BUT I HAVEN'T COME UP WITH AN ANSWER. I JUST FLT OUT MISSED THE TFC.

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.