Near midair collision indicated on TCASII.

Attributes
ACN	300558
Time
Date	199503
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : gyy
State Reference	IN
Altitude	msl bound lower : 5000 msl bound upper : 6000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ord
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	other : unknown
Flight Phase	climbout : intermediate altitude cruise other cruise other
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 200 flight time total : 11000 flight time type : 4000
ASRS Report	300558
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : nmac non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 0 vertical : 300
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were on an assigned heading to intercept mdw runway 31C localizer, assigned altitude was 5000 ft (at pilot's discretion). We were level at 5000 ft. I saw gary airport below us on the right side 3-5 NM through broken clouds. We received a TA and the TCASII showed 2 targets at 1 O'clock, 300 ft below and climbing. Subsequently got a climb RA and captain initiated climb to 6000 ft while I advised ATC. ATC said target was level at 4000 ft, but subsequently he determined traffic was at 5000 ft. I don't know why the controller got no conflict alert, but I think TCASII saved us from a midair collision or a very near miss. Never saw other aircraft due to IMC. Don't know if there were really 2 aircraft of just 1.

Original NASA ASRS Text

Title: NMAC INDICATED ON TCASII.

Narrative: WE WERE ON AN ASSIGNED HDG TO INTERCEPT MDW RWY 31C LOC, ASSIGNED ALT WAS 5000 FT (AT PLT'S DISCRETION). WE WERE LEVEL AT 5000 FT. I SAW GARY ARPT BELOW US ON THE R SIDE 3-5 NM THROUGH BROKEN CLOUDS. WE RECEIVED A TA AND THE TCASII SHOWED 2 TARGETS AT 1 O'CLOCK, 300 FT BELOW AND CLBING. SUBSEQUENTLY GOT A CLB RA AND CAPT INITIATED CLB TO 6000 FT WHILE I ADVISED ATC. ATC SAID TARGET WAS LEVEL AT 4000 FT, BUT SUBSEQUENTLY HE DETERMINED TFC WAS AT 5000 FT. I DON'T KNOW WHY THE CTLR GOT NO CONFLICT ALERT, BUT I THINK TCASII SAVED US FROM A MIDAIR COLLISION OR A VERY NEAR MISS. NEVER SAW OTHER ACFT DUE TO IMC. DON'T KNOW IF THERE WERE REALLY 2 ACFT OF JUST 1.

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.