<< >> NASA ASRS Report 415589, October 1998

ARTCC controller at ZAU sequencing 2 arrs discontinued vertical separation before horizontal separation was established.

Attributes
ACN	415589
Time
Date	199810
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : oxi
State Reference	IL
Altitude	msl bound lower : 15600 msl bound upper : 15600
Environment
Flight Conditions	Marginal
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zau tracon : hts
Operator	common carrier : air carrier
Make Model Name	MD-80 Series (DC-9-80) Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	descent other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	MD-80 Series (DC-9-80) Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller non radar : 1 controller radar : 19
ASRS Report	415589
Person 2
Affiliation	government : faa
Function	controller : non radar
Qualification	controller : radar
Experience	controller radar : 5
ASRS Report	415705
Events
Anomaly	conflict : airborne less severe 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 none taken : detected after the fact other
Consequence	faa : investigated
Miss Distance	horizontal : 27600 vertical : 400
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

I was sequencing these 2 arrival aircraft on the oxi 3 and okk 1 STAR, 9 mi northwest of oxi VOR. The aircraft were assigned 300 KTS and I thought I had 5 mi horizontal separation when I discontinued vertical separation. Supplemental information from acn 415705: I was the manual controller during an arrival rush to ord. We were running a 7 mi in trail, 300 KT problem. We had the aircraft tight (5-7 mi in trail) with comparable speeds. We had 2 target jumps that put the aircraft in closer proximity than they should have been. I feel that bad radar displays were the culprit in this situation.

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Original NASA ASRS Text

Title: ARTCC CTLR AT ZAU SEQUENCING 2 ARRS DISCONTINUED VERT SEPARATION BEFORE HORIZ SEPARATION WAS ESTABLISHED.

Narrative: I WAS SEQUENCING THESE 2 ARR ACFT ON THE OXI 3 AND OKK 1 STAR, 9 MI NW OF OXI VOR. THE ACFT WERE ASSIGNED 300 KTS AND I THOUGHT I HAD 5 MI HORIZ SEPARATION WHEN I DISCONTINUED VERT SEPARATION. SUPPLEMENTAL INFO FROM ACN 415705: I WAS THE MANUAL CTLR DURING AN ARR RUSH TO ORD. WE WERE RUNNING A 7 MI IN TRAIL, 300 KT PROB. WE HAD THE ACFT TIGHT (5-7 MI IN TRAIL) WITH COMPARABLE SPDS. WE HAD 2 TARGET JUMPS THAT PUT THE ACFT IN CLOSER PROX THAN THEY SHOULD HAVE BEEN. I FEEL THAT BAD RADAR DISPLAYS WERE THE CULPRIT IN THIS SIT.

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.