B737-700 captain reported an near midair collision with a light aircraft in the vicinity of mdw.

Attributes
ACN	1564205
Time
Date	201807
Local Time Of Day	0601-1200
Place
Locale Reference	C90.TRACON
State Reference	IL
Environment
Light	Daylight
Aircraft 1
Make Model Name	B737-700
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Flight Plan	IFR
Aircraft 2
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 91
Flight Phase	Cruise
Person 1
Function	Captain Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 423 Flight Crew Type 423
Events
Anomaly	Conflict NMAC
Miss Distance	Horizontal 500 Vertical 100

Narrative:

We were level at 5000 ft on the endee 4 arrival into mdw just before kempz when ATC gave us a traffic call with 'type and altitude unknown.' about a minute later with still no TCAS alert or symbol; we visually acquired a low wing general aviation aircraft heading southeast left to right approximately 100 ft low; less than a mile in front of us. We disengaged the autopilot and executed a turn to the left to avoid. We estimate we cleared him by 100 ft vertically and 500 ft feet laterally. We contacted ATC and continued uneventfully. After the flight we did not get any questions from the passengers or flight attendants. I don't think they even noticed. I called dispatch to report the event. We feel we did everything correctly and just wished all GA aircraft were more aware of jet traffic flight paths and got flight following everywhere they went.

Original NASA ASRS Text

Title: B737-700 Captain reported an NMAC with a light aircraft in the vicinity of MDW.

Narrative: We were level at 5000 ft on the ENDEE 4 Arrival into MDW just before KEMPZ when ATC gave us a traffic call with 'type and altitude unknown.' About a minute later with still no TCAS alert or symbol; we visually acquired a low wing general aviation aircraft heading southeast left to right approximately 100 ft low; less than a mile in front of us. We disengaged the autopilot and executed a turn to the left to avoid. We estimate we cleared him by 100 ft vertically and 500 ft feet laterally. We contacted ATC and continued uneventfully. After the flight we did not get any questions from the passengers or Flight Attendants. I don't think they even noticed. I called Dispatch to report the event. We feel we did everything correctly and just wished all GA aircraft were more aware of jet traffic flight paths and got flight following everywhere they went.

Data retrieved from NASA's ASRS site 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.