Less than standard separation between 2 corp aircraft. Operational error.

Attributes
ACN	98962
Time
Date	198811
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : svm
State Reference	MI
Altitude	msl bound lower : 28000 msl bound upper : 28500
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zob tower : phf
Operator	general aviation : corporate
Make Model Name	Small Transport, Low Wing, 2 Turboprop Eng
Flight Phase	cruise other
Flight Plan	IFR
Aircraft 2
Operator	general aviation : corporate
Make Model Name	Light Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
ASRS Report	98962
Person 2
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance none taken : insufficient time other
Consequence	faa : investigated
Miss Distance	horizontal : 27000 vertical : 500
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Corp X was wbound at FL280 and corp Y was eastbound at FL290. Y was cleared to FL260 and the 5 mile protection was lost. Both aircraft were given hard 90 degree turns. Both pilots were cleared on course with no concern. I had a system error and the concern is here at cleveland ARTCC. I discovered the problem before the conflict alert went off. No evasive action was taken. The big problem was data block overlay. The traffic load at the sector was moderate. I have no suggestions as to how to prevent this system error, except less traffic load.

Original NASA ASRS Text

Title: LESS THAN STANDARD SEPARATION BETWEEN 2 CORP ACFT. OPERATIONAL ERROR.

Narrative: CORP X WAS WBOUND AT FL280 AND CORP Y WAS EBND AT FL290. Y WAS CLRED TO FL260 AND THE 5 MILE PROTECTION WAS LOST. BOTH ACFT WERE GIVEN HARD 90 DEG TURNS. BOTH PLTS WERE CLRED ON COURSE WITH NO CONCERN. I HAD A SYS ERROR AND THE CONCERN IS HERE AT CLEVELAND ARTCC. I DISCOVERED THE PROBLEM BEFORE THE CONFLICT ALERT WENT OFF. NO EVASIVE ACTION WAS TAKEN. THE BIG PROB WAS DATA BLOCK OVERLAY. THE TFC LOAD AT THE SECTOR WAS MODERATE. I HAVE NO SUGGESTIONS AS TO HOW TO PREVENT THIS SYS ERROR, EXCEPT LESS TFC LOAD.

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.