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

Attributes
ACN	129044
Time
Date	198911
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : pmm
State Reference	MI
Altitude	msl bound lower : 20000 msl bound upper : 21000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zau
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	descent other other
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller military : 4 controller non radar : 2 controller radar : 3
ASRS Report	129044
Person 2
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	conflict : airborne less severe non adherence : published procedure non adherence : required legal separation other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance
Consequence	Other
Miss Distance	horizontal : 12000 vertical : 0
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error Intra Facility Coordination Failure

Narrative:

Aircraft X was at FL210 on top of aircraft Y at FL200. Aircraft X was to have been descended to 3000', aircraft Y to be descended to 10000' as per ord LOA. Pmm hi controller did not get aircraft X below. The pmm hi controller never coordinated aircraft X at FL210 on top of aircraft Y at FL200. He descended the aircraft and just handed them off. Only had 7 aircraft, but at the time 2 were holding high because they could not take the runway in use at this arrival fix. As the second holding aircraft was being turned, approach called and requested one more turn inbound. At same time aircraft X and Y were switched late and close to boundary. In a hurry to descend aircraft X to 3000' under aircraft Y in hold, I thought that aircraft X was at FL200 and aircraft Y at FL210, which is how they should have been. I realized too late to provide required sep. Due to sudden workload and sector complexity, I was unable to realize that there would be a loss of sep until it was too late. Aircraft X was 3 mi in front of aircraft Y. When aircraft X started down, it was too late. I had to turn both aircraft.

Original NASA ASRS Text

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

Narrative: ACFT X WAS AT FL210 ON TOP OF ACFT Y AT FL200. ACFT X WAS TO HAVE BEEN DSNDED TO 3000', ACFT Y TO BE DSNDED TO 10000' AS PER ORD LOA. PMM HI CTLR DID NOT GET ACFT X BELOW. THE PMM HI CTLR NEVER COORDINATED ACFT X AT FL210 ON TOP OF ACFT Y AT FL200. HE DSNDED THE ACFT AND JUST HANDED THEM OFF. ONLY HAD 7 ACFT, BUT AT THE TIME 2 WERE HOLDING HIGH BECAUSE THEY COULD NOT TAKE THE RWY IN USE AT THIS ARR FIX. AS THE SECOND HOLDING ACFT WAS BEING TURNED, APCH CALLED AND REQUESTED ONE MORE TURN INBND. AT SAME TIME ACFT X AND Y WERE SWITCHED LATE AND CLOSE TO BOUNDARY. IN A HURRY TO DSND ACFT X TO 3000' UNDER ACFT Y IN HOLD, I THOUGHT THAT ACFT X WAS AT FL200 AND ACFT Y AT FL210, WHICH IS HOW THEY SHOULD HAVE BEEN. I REALIZED TOO LATE TO PROVIDE REQUIRED SEP. DUE TO SUDDEN WORKLOAD AND SECTOR COMPLEXITY, I WAS UNABLE TO REALIZE THAT THERE WOULD BE A LOSS OF SEP UNTIL IT WAS TOO LATE. ACFT X WAS 3 MI IN FRONT OF ACFT Y. WHEN ACFT X STARTED DOWN, IT WAS TOO LATE. I HAD TO TURN BOTH ACFT.

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.