EMB145 flight crew has a TCAS RA during descent on the oxi.OXI3 to ord.

Attributes
ACN	707072
Time
Date	200608
Local Time Of Day	0601 To 1200
Place
Locale Reference	navaid : oxi.vor
State Reference	IN
Altitude	msl single value : 11600
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : c90.tracon
Operator	common carrier : air carrier
Make Model Name	EMB ERJ 145 ER&LR
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : intermediate altitude
Route In Use	arrival star : oxi
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tracon : c90.tracon
Operator	general aviation : personal
Make Model Name	Beechcraft Twin Turboprop Jet Undifferentiated or Other Model
Operating Under FAR Part	Part 91
Navigation In Use	other
Flight Phase	cruise : level
Flight Plan	VFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain
Qualification	pilot : atp pilot : cfi pilot : flight engineer
Experience	flight time last 90 days : 220 flight time total : 8700 flight time type : 6800
ASRS Report	707072
Person 2
Affiliation	other
Function	flight crew : single pilot
Events
Anomaly	conflict : nmac non adherence : required legal separation
Independent Detector	aircraft equipment : tcas other controllerb other flight crewa
Resolutory Action	controller : issued advisory flight crew : took precautionary avoidance action
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 300 vertical : 200
Supplementary
Problem Areas	Flight Crew Human Performance ATC Human Performance Airspace Structure
Primary Problem	Ambiguous

Narrative:

During descent on the OKK1 arrival to ord; the center controller advised us of traffic 5 mi ahead at 11500 ft. We were at approximately 12000 ft in a descent to 11000 ft when this call was made. A few seconds late we got a TA that immediately escalated to an RA (descend). We responded and at the conclusion of the RA our altitude was 10600 ft. We advised the controller and returned to altitude when clear of conflict. I believe the biggest factor in this incident was the VFR (I believe) aircraft choosing to cruise at an arrival gate for ord at the required gate entry altitude per TRACON. While I relish the ability to fly VFR; these areas need to be published as high density traffic areas; and possible collision areas as well as altitudes.

Original NASA ASRS Text

Title: EMB145 FLT CREW HAS A TCAS RA DURING DSCNT ON THE OXI.OXI3 TO ORD.

Narrative: DURING DSCNT ON THE OKK1 ARR TO ORD; THE CTR CTLR ADVISED US OF TFC 5 MI AHEAD AT 11500 FT. WE WERE AT APPROX 12000 FT IN A DSCNT TO 11000 FT WHEN THIS CALL WAS MADE. A FEW SECONDS LATE WE GOT A TA THAT IMMEDIATELY ESCALATED TO AN RA (DSND). WE RESPONDED AND AT THE CONCLUSION OF THE RA OUR ALT WAS 10600 FT. WE ADVISED THE CTLR AND RETURNED TO ALT WHEN CLR OF CONFLICT. I BELIEVE THE BIGGEST FACTOR IN THIS INCIDENT WAS THE VFR (I BELIEVE) ACFT CHOOSING TO CRUISE AT AN ARR GATE FOR ORD AT THE REQUIRED GATE ENTRY ALT PER TRACON. WHILE I RELISH THE ABILITY TO FLY VFR; THESE AREAS NEED TO BE PUBLISHED AS HIGH DENSITY TFC AREAS; AND POSSIBLE COLLISION AREAS AS WELL AS ALTS.

Data retrieved from NASA's ASRS site as of January 2009 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.