ZOB controller experienced operational error at FL310 when issued discretionary descent.

Attributes
ACN	634169
Time
Date	200410
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	navaid : djb.vortac
State Reference	OH
Altitude	msl single value : 31000
Environment
Light	Night
Aircraft 1
Controlling Facilities	artcc : zob.artcc tower : dtw.tower
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	descent : intermediate altitude
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zob.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 : 20
ASRS Report	634169
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation
Independent Detector	other controllera
Resolutory Action	flight crew : took evasive action
Consequence	faa : investigated
Miss Distance	horizontal : 21600 vertical : 900
Supplementary
Problem Areas	ATC Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Aircraft X was given discretionary descent from FL310 to FL290 landing pit came into conflict with aircraft Y in sector above.

Original NASA ASRS Text

Title: ZOB CTLR EXPERIENCED OPERROR AT FL310 WHEN ISSUED DISCRETIONARY DSCNT.

Narrative: ACFT X WAS GIVEN DISCRETIONARY DSCNT FROM FL310 TO FL290 LNDG PIT CAME INTO CONFLICT WITH ACFT Y IN SECTOR ABOVE.

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.