Air carrier X had less than standard separation from cpr Y. System error.

Attributes
ACN	137115
Time
Date	199002
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : dbl
State Reference	CO
Altitude	msl bound lower : 20000 msl bound upper : 20000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdv
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	enroute : direct
Flight Plan	IFR
Aircraft 2
Operator	general aviation : corporate
Make Model Name	Light Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller non radar : 6 controller radar : 10
ASRS Report	137115
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
Resolutory Action	none taken : detected after the fact
Consequence	faa : investigated
Miss Distance	horizontal : 9000 vertical : 300
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Cpr Y, light transport corporate, IFR. Air carrier X was inbound wanting a visual approach (quick let down). Cpr Y, outbnd, was southbound level at FL190 attempting to minimize the time I would have to delay air carrier X. I issued traffic (which he confirmed was in sight) and when I observed the beacon slash pass the projected flight path of cpr Y, I issued a descent clearance. After issuing traffic and prior to issuing the descent clearance I had a couple of things to take care of (landline and strip marking). I didn't monitor the mode C readout during this phase. I quickly looked at the beacon slash and believed them to have passed. I issued the descent clearance without doublechking the full data tags including altitude readout so I'm not sure if I anticipated the crossing and/or air carrier X began descent early and I didn't catch it.

Original NASA ASRS Text

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

Narrative: CPR Y, LTT CORPORATE, IFR. ACR X WAS INBND WANTING A VISUAL APCH (QUICK LET DOWN). CPR Y, OUTBND, WAS SBND LEVEL AT FL190 ATTEMPTING TO MINIMIZE THE TIME I WOULD HAVE TO DELAY ACR X. I ISSUED TFC (WHICH HE CONFIRMED WAS IN SIGHT) AND WHEN I OBSERVED THE BEACON SLASH PASS THE PROJECTED FLT PATH OF CPR Y, I ISSUED A DSCNT CLRNC. AFTER ISSUING TFC AND PRIOR TO ISSUING THE DSCNT CLRNC I HAD A COUPLE OF THINGS TO TAKE CARE OF (LANDLINE AND STRIP MARKING). I DIDN'T MONITOR THE MODE C READOUT DURING THIS PHASE. I QUICKLY LOOKED AT THE BEACON SLASH AND BELIEVED THEM TO HAVE PASSED. I ISSUED THE DSCNT CLRNC WITHOUT DOUBLECHKING THE FULL DATA TAGS INCLUDING ALT READOUT SO I'M NOT SURE IF I ANTICIPATED THE XING AND/OR ACR X BEGAN DSCNT EARLY AND I DIDN'T CATCH IT.

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.