C90 controller described a potential conflict event involving two IFR aircraft; noting the lack of t...

Narrative:

An E120 was being vectored to gyy airport for landing. He was on a 090 heading and cleared to descend from 5;000 ft to 3;000 ft. The E120 descended slowly after being given a descent clearance. An airline jet was opposite direction at 4;000 being vectored to land at mdw on a 270 heading. I noticed the conflict as the E120 was descending through 4;000 and issued vectors to both aircraft to avoid a conflict. The E120 then stated he had the traffic in sight and would maintain visual separation as he expedited the descent to 3;000. Minimal separation was maintained. There was no indication by either pilot of TCAS advisories. An earlier indication of automated conflict alert may have brought my attention to the conflict sooner. The conflict alert did not activate until the aircraft were already on evasive headings and were way past a time when the alarm would have been useful.

Original NASA ASRS Text

Title: C90 Controller described a potential conflict event involving two IFR aircraft; noting the lack of timely Conflict Alert activation during this instance.

Narrative: An E120 was being vectored to GYY airport for landing. He was on a 090 heading and cleared to descend from 5;000 FT to 3;000 FT. The E120 descended slowly after being given a descent clearance. An airline jet was opposite direction at 4;000 being vectored to land at MDW on a 270 heading. I noticed the conflict as the E120 was descending through 4;000 and issued vectors to both aircraft to avoid a conflict. The E120 then stated he had the traffic in sight and would maintain visual separation as he expedited the descent to 3;000. Minimal separation was maintained. There was no indication by either pilot of TCAS advisories. An earlier indication of Automated Conflict Alert may have brought my attention to the conflict sooner. The Conflict Alert did not activate until the aircraft were already on evasive headings and were way past a time when the alarm would have been useful.

Data retrieved from NASA's ASRS site as of April 2012 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.

Attributes
ACN	935100
Time
Date	201103
Local Time Of Day	0001-0600
Place
Locale Reference	C90.TRACON
State Reference	IL
Aircraft 1
Make Model Name	Brasilia EMB-120 All Series
Operating Under FAR Part	Part 121
Flight Phase	Descent
Route In Use	Vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Route In Use	Vectors
Person 1
Function	Departure
Qualification	Air Traffic Control Developmental
Events
Anomaly	ATC Issue All Types Conflict Airborne Conflict

C90 controller described a potential conflict event involving two IFR aircraft; noting the lack of timely conflict alert activation during this instance.