Less than standard separation between aircraft X and aircraft Y. System error.

Attributes
ACN	281648
Time
Date	199408
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : iow
State Reference	IA
Altitude	msl bound lower : 33000 msl bound upper : 33000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zau
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	other : unknown
Flight Phase	cruise other
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	other : unknown
Flight Phase	cruise other descent other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 23
ASRS Report	281648
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	conflict : airborne less severe non adherence : published procedure non adherence : required legal separation
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Miss Distance	horizontal : 21600 vertical : 900
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Aircraft #1 was level FL350 en route gsh direct dsm aircraft #2 was level FL330 en route alo direct low then southeast. Clearance was given to aircraft #1 to descend to FL330. When he started down he was changed to the next frequency. Shortly thereafter the potential conflict was noticed. I went to the sector controling #1 and told the controller to climb back to FL350. At the same time I checked his scope (he owned FL310 and below and I owned FL330 and above) to make sure FL310 was clear. I then descended aircraft #2. The cause of the problem was my failure to notice the potential conflict. This was compounded by the aircraft being on different frequencys.

Original NASA ASRS Text

Title: LTSS BTWN ACFT X AND ACFT Y. SYS ERROR.

Narrative: ACFT #1 WAS LEVEL FL350 ENRTE GSH DIRECT DSM ACFT #2 WAS LEVEL FL330 ENRTE ALO DIRECT LOW THEN SE. CLRNC WAS GIVEN TO ACFT #1 TO DSND TO FL330. WHEN HE STARTED DOWN HE WAS CHANGED TO THE NEXT FREQ. SHORTLY THEREAFTER THE POTENTIAL CONFLICT WAS NOTICED. I WENT TO THE SECTOR CTLING #1 AND TOLD THE CTLR TO CLB BACK TO FL350. AT THE SAME TIME I CHKED HIS SCOPE (HE OWNED FL310 AND BELOW AND I OWNED FL330 AND ABOVE) TO MAKE SURE FL310 WAS CLR. I THEN DSNDED ACFT #2. THE CAUSE OF THE PROB WAS MY FAILURE TO NOTICE THE POTENTIAL CONFLICT. THIS WAS COMPOUNDED BY THE ACFT BEING ON DIFFERENT FREQS.

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.