ZOB controller experienced operational error at FL310 misjudging lateral separation.

Attributes
ACN	632347
Time
Date	200408
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	navaid : vwv.vor
State Reference	OH
Altitude	msl bound lower : 31000 msl bound upper : 35000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zob.artcc
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zob.artcc
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise : enroute altitude change descent : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 15
ASRS Report	632347
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	controller : issued new clearance flight crew : took evasive action
Consequence	faa : investigated
Miss Distance	horizontal : 6000 vertical : 1300
Supplementary
Problem Areas	ATC Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

I misjudged lateral separation and descended air carrier Y through the flight path of air carrier X. When I realized I would lose lateral, I climbed air carrier Y back up and descended air carrier X. Air carrier Y was en route to mdw and I thought he was established in J60 but was not. Air carrier Y was at FL350 wbound and air carrier X was eastbound at FL330. I descended air carrier Y thinking they were separated. They obviously were not.

Original NASA ASRS Text

Title: ZOB CTLR EXPERIENCED OPERROR AT FL310 MISJUDGING LATERAL SEPARATION.

Narrative: I MISJUDGED LATERAL SEPARATION AND DSNDED ACR Y THROUGH THE FLT PATH OF ACR X. WHEN I REALIZED I WOULD LOSE LATERAL, I CLBED ACR Y BACK UP AND DSNDED ACR X. ACR Y WAS ENRTE TO MDW AND I THOUGHT HE WAS ESTABLISHED IN J60 BUT WAS NOT. ACR Y WAS AT FL350 WBOUND AND ACR X WAS EBOUND AT FL330. I DSNDED ACR Y THINKING THEY WERE SEPARATED. THEY OBVIOUSLY WERE NOT.

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.