Air carrier Y had less than standard separation from air carrier X. System error.

Attributes
ACN	127889
Time
Date	198911
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : msp
State Reference	MN
Altitude	msl bound lower : 10000 msl bound upper : 11000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zmp tower : bwi
Operator	common carrier : air carrier
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 16
ASRS Report	127889
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation non adherence : published procedure
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	controller : issued new clearance other
Consequence	faa : investigated
Miss Distance	horizontal : 24000 vertical : 700
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Air carrier X was level at 10,000 on way into msp. He was probably slowing. Air carrier Y was in trail reducing speed and had been turned for additional space. Air carrier Y overran air carrier X before I realized he was so close. Air carrier Y was still descending and I recleared him to 11,000 as he was going through it.

Original NASA ASRS Text

Title: ACR Y HAD LESS THAN STANDARD SEPARATION FROM ACR X. SYSTEM ERROR.

Narrative: ACR X WAS LEVEL AT 10,000 ON WAY INTO MSP. HE WAS PROBABLY SLOWING. ACR Y WAS IN TRAIL REDUCING SPEED AND HAD BEEN TURNED FOR ADDITIONAL SPACE. ACR Y OVERRAN ACR X BEFORE I REALIZED HE WAS SO CLOSE. ACR Y WAS STILL DESCENDING AND I RECLEARED HIM TO 11,000 AS HE WAS GOING THROUGH IT.

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.