Air carrier was descended to an occupied altitude resulting in less than standard separation.

Attributes
ACN	137550
Time
Date	199002
Day	Sat
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : mcw
State Reference	IA
Altitude	msl bound lower : 31000 msl bound upper : 32400
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zmp
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	cruise other descent other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 22 controller supervisory : 2
ASRS Report	137550
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	non adherence : published procedure non adherence : required legal separation
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	controller : issued new clearance
Consequence	Other
Miss Distance	horizontal : 24000 vertical : 1400
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

I descended air carrier X to FL310, who then left FL330. I then descended air carrier Y to FL240. He did not leave FL310 immediately. I instructed him to start down. I asked air carrier X to maintain FL330. He stopped descent at FL324 and climbed. They passed with 4 mi and 1400'.

Original NASA ASRS Text

Title: ACR WAS DESCENDED TO AN OCCUPIED ALT RESULTING IN LESS THAN STANDARD SEPARATION.

Narrative: I DSNDED ACR X TO FL310, WHO THEN LEFT FL330. I THEN DSNDED ACR Y TO FL240. HE DID NOT LEAVE FL310 IMMEDIATELY. I INSTRUCTED HIM TO START DOWN. I ASKED ACR X TO MAINTAIN FL330. HE STOPPED DSCNT AT FL324 AND CLBED. THEY PASSED WITH 4 MI AND 1400'.

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.