ZKC ARTCC controller misjudged spacing with conflicting traffic when issuing descent clearance.

Attributes
ACN	573719
Time
Date	200302
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : brl.airport
State Reference	IA
Altitude	msl bound lower : 33000 msl bound upper : 35000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zkc.artcc
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	cruise : enroute altitude change
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zkc.artcc
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 14 controller time certified in position2 : 4
ASRS Report	573719
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	conflict : airborne critical non adherence : required legal separation
Independent Detector	atc equipment : conflict alert aircraft equipment : tcas other controllera
Resolutory Action	none taken : insufficient time
Consequence	faa : investigated
Miss Distance	horizontal : 12000 vertical : 600
Supplementary
Problem Areas	ATC Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

At approximately XA57Z I issued air carrier X a crossing restr to cross keokk intersection at FL330. At this time air carrier X was at FL390 and approximately over kirkville, mo. A couple of mins later I noticed arc X was going to conflict with air carrier Y at FL330. I then cleared air carrier X to begin their descent now and maintain FL350. At XB03Z air carrier X descended below FL350 and, subsequently, separation was lost with air carrier Y. As I understand it air carrier Y took an RA action and descended. A change in controllers had occurred between air carrier X receiving the FL350 clearance and the separation error with air carrier Y.

Original NASA ASRS Text

Title: ZKC ARTCC CTLR MISJUDGED SPACING WITH CONFLICTING TFC WHEN ISSUING DSCNT CLRNC.

Narrative: AT APPROX XA57Z I ISSUED ACR X A XING RESTR TO CROSS KEOKK INTXN AT FL330. AT THIS TIME ACR X WAS AT FL390 AND APPROX OVER KIRKVILLE, MO. A COUPLE OF MINS LATER I NOTICED ARC X WAS GOING TO CONFLICT WITH ACR Y AT FL330. I THEN CLRED ACR X TO BEGIN THEIR DSCNT NOW AND MAINTAIN FL350. AT XB03Z ACR X DSNDED BELOW FL350 AND, SUBSEQUENTLY, SEPARATION WAS LOST WITH ACR Y. AS I UNDERSTAND IT ACR Y TOOK AN RA ACTION AND DSNDED. A CHANGE IN CTLRS HAD OCCURRED BTWN ACR X RECEIVING THE FL350 CLRNC AND THE SEPARATION ERROR WITH ACR Y.

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.