Air carrier Y descent through occupied altitude had less than standard separation from air carrier Y...

Attributes
ACN	300149
Time
Date	199503
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : lan
State Reference	MI
Altitude	msl bound lower : 29000 msl bound upper : 30700
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zau artcc : zob
Operator	common carrier : air carrier
Make Model Name	DC-9 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	descent other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller non radar : 13 controller radar : 11 flight time total : 390
ASRS Report	300149
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	faa : investigated
Miss Distance	horizontal : 24000 vertical : 1000
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error Inter Facility Coordination Failure

Narrative:

I was working the pmm high sector at ZAU. I had switched air carrier X, a dc-9, mke J34 crl ewr at FL290 to ZOB approximately 2 mins before the incident. I had the handoff on air carrier Y, BJ3J, hpn fnt J94 pmm PMM3 ord at FL310 when I switched X to ZOB. Y was in the middle of a small ord push (10-15 aircraft) during which at least 1/2 the inbounds were at FL280 or descending to FL280. I first noticed a problem when the aircraft were about 7 mi apart and I observed X out of FL307 descending. I broadcast to see if I had Y and when I realized I did not, I called for the supervisor. I did not call ZOB because I felt that would only confuse the situation. I feel the situation was caused by ZOB inadvertently descending Y. They had not entered FL280 in the computer, had not aprequed the altitude and the descent was at a very inopportune time, so I feel the confused X with another aircraft. ZOB actually took the aircraft back to FL300 after the incident occurred.

Original NASA ASRS Text

Title: ACR Y DSCNT THROUGH OCCUPIED ALT HAD LTSS FROM ACR Y. SYS ERROR.

Narrative: I WAS WORKING THE PMM HIGH SECTOR AT ZAU. I HAD SWITCHED ACR X, A DC-9, MKE J34 CRL EWR AT FL290 TO ZOB APPROX 2 MINS BEFORE THE INCIDENT. I HAD THE HDOF ON ACR Y, BJ3J, HPN FNT J94 PMM PMM3 ORD AT FL310 WHEN I SWITCHED X TO ZOB. Y WAS IN THE MIDDLE OF A SMALL ORD PUSH (10-15 ACFT) DURING WHICH AT LEAST 1/2 THE INBOUNDS WERE AT FL280 OR DSNDING TO FL280. I FIRST NOTICED A PROB WHEN THE ACFT WERE ABOUT 7 MI APART AND I OBSERVED X OUT OF FL307 DSNDING. I BROADCAST TO SEE IF I HAD Y AND WHEN I REALIZED I DID NOT, I CALLED FOR THE SUPVR. I DID NOT CALL ZOB BECAUSE I FELT THAT WOULD ONLY CONFUSE THE SIT. I FEEL THE SIT WAS CAUSED BY ZOB INADVERTENTLY DSNDING Y. THEY HAD NOT ENTERED FL280 IN THE COMPUTER, HAD NOT APREQUED THE ALT AND THE DSCNT WAS AT A VERY INOPPORTUNE TIME, SO I FEEL THE CONFUSED X WITH ANOTHER ACFT. ZOB ACTUALLY TOOK THE ACFT BACK TO FL300 AFTER THE INCIDENT OCCURRED.

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.

Air carrier Y descent through occupied altitude had less than standard separation from air carrier Y. System error.