Encountered small aircraft unreported traffic and apparently not using a transponder.

Attributes
ACN	97570
Time
Date	198811
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : jot
State Reference	IL
Altitude	msl bound lower : 5000 msl bound upper : 5050
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ord
Operator	common carrier : air carrier
Make Model Name	Light Transport, High Wing, 2 Turboprop Eng
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Aircraft 2
Operator	general aviation : personal
Make Model Name	Small Aircraft, High Wing, 1 Eng, Fixed Gear
Flight Phase	cruise other descent other
Route In Use	enroute : direct
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 3520
ASRS Report	97570
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	conflict : nmac
Independent Detector	other flight crewa
Resolutory Action	flight crew : took evasive action
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 0 vertical : 50
Supplementary
Primary Problem	Flight Crew Human Performance

Narrative:

On a flight from rfd to mdw we were cleared direct to the joliet VOR at 5000'. At approximately 25-30 DME from the VOR the first officer, who was the PF, pulled the nose of the aircraft up and to the left to avoid an small aircraft that then passed approximately 50' directly under our aircraft. We were on a heading of about 140 degrees direct to the VOR. The small aircraft approached us from about our 2-3 O'clock position, passed under, then departed our area at about our 8-9 O'clock--also at 5000' headed toward the northeast. The first officer's reaction then following control movement appeared to be enough to startle everyone on board, but not enough to cause passenger or articles to be moved from their resting place. There also was no aircraft damage. Shortly after the incident I informed the approach controller that I had passed within 50' of an small aircraft. He thanked me for the report and told me he showed no traffic in my area. There was no further mention of the incident on the frequency.

Original NASA ASRS Text

Title: ENCOUNTERED SMA UNREPORTED TRAFFIC AND APPARENTLY NOT USING A TRANSPONDER.

Narrative: ON A FLT FROM RFD TO MDW WE WERE CLRED DIRECT TO THE JOLIET VOR AT 5000'. AT APPROX 25-30 DME FROM THE VOR THE F/O, WHO WAS THE PF, PULLED THE NOSE OF THE ACFT UP AND TO THE LEFT TO AVOID AN SMA THAT THEN PASSED APPROX 50' DIRECTLY UNDER OUR ACFT. WE WERE ON A HDG OF ABOUT 140 DEGS DIRECT TO THE VOR. THE SMA APCHED US FROM ABOUT OUR 2-3 O'CLOCK POS, PASSED UNDER, THEN DEPARTED OUR AREA AT ABOUT OUR 8-9 O'CLOCK--ALSO AT 5000' HEADED TOWARD THE NE. THE F/O'S REACTION THEN FOLLOWING CONTROL MOVEMENT APPEARED TO BE ENOUGH TO STARTLE EVERYONE ON BOARD, BUT NOT ENOUGH TO CAUSE PAX OR ARTICLES TO BE MOVED FROM THEIR RESTING PLACE. THERE ALSO WAS NO ACFT DAMAGE. SHORTLY AFTER THE INCIDENT I INFORMED THE APCH CTLR THAT I HAD PASSED WITHIN 50' OF AN SMA. HE THANKED ME FOR THE RPT AND TOLD ME HE SHOWED NO TFC IN MY AREA. THERE WAS NO FURTHER MENTION OF THE INCIDENT ON THE FREQ.

Data retrieved from NASA's ASRS site as of August 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.