Narrative:

While being vectored for a visual runway 4R at mdw; we experienced a traffic conflict which could have easily led to a midair collision. We were approximately 3-5 mi south of the runway 4R approach course at 3000 ft MSL; heading 270 degrees; 170 KTS. I noticed an aircraft on TCAS and noted it was co-altitude approximately 3 mi at 11 O'clock position. Soon thereafter; ATC issued a traffic alert for an aircraft at '12 O'clock position; 2 mi; co-altitude' and recommended a climb if not in sight. I acquired the aircraft (a C172 or similar); told the first officer I had it in sight and was climbing to avoid it. I initiated a climb to 3500 ft MSL and then ATC directed a turn to 010 degrees to intercept. During the turn we crossed directly over the aircraft. The first officer eventually got the aircraft in sight and indicated to me that it was turning back towards us after we had flown over him. Per the first officer's comments that it was eventually safe to begin a descent; I started down; intercepted final and continued the approach without further incident. The TCAS system had given us a TA; but no RA. Apparently we initiated the climb before it decided to issue an RA. This is the second time this type of incident has occurred in the short time since I have been a captain at company (upgraded almost 1 yr ago). Here is the bottom line. There is going to be a midair collision in chicago. It is only a question of when; not if. The cessna which caused this event was outside of controled airspace and not in radio contact with approach. He/she was perfectly legal to be there. The problem is; legal or not; it was stupid. Since it is impossible to legislate common sense; something needs to be done about allowing these GA aircraft to fly within a few mi of the final approach course at the same altitudes we are being vectored at. I don't care if it is a VFR corridor below our vectoring altitudes or a change in mdw's airspace; but something needs to change now. The FAA; as it has proven time and again; will not be proactive until there is a body count. I strongly recommend our company and chicago ATC push this issue until the FAA realizes how asinine this practice is. Simply hoping that the inevitable burning hulk of an airplane doesn't have our company name written on its tail will lead to a billion plus dollar mistake. The airspace at mdw needs to change now! There is absolutely no sane reason to allow GA VFR aircraft to fly right through approach corridors at any airport without talking to somebody. Human error is the most common cause of aircraft accidents today. In both incidents that have happened to me; it was only the human factor that saved a collision. This time; thankfully; both the controller and I recognized the threat. The first time it happened; the controller was too busy to notify me of the threat. What happens next time when both the controller and the crew are task saturated?

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Original NASA ASRS Text

Title: B737 FLT CREW CLIMBS TO AVOID C172 AT 3000 FEET DISPLAYED ON TCAS AND REPORTED BY ATC SW OF MDW JUST OUTSIDE THE CLASS C AND BELOW THE CLASS B.

Narrative: WHILE BEING VECTORED FOR A VISUAL RWY 4R AT MDW; WE EXPERIENCED A TFC CONFLICT WHICH COULD HAVE EASILY LED TO A MIDAIR COLLISION. WE WERE APPROX 3-5 MI S OF THE RWY 4R APCH COURSE AT 3000 FT MSL; HDG 270 DEGS; 170 KTS. I NOTICED AN ACFT ON TCAS AND NOTED IT WAS CO-ALT APPROX 3 MI AT 11 O'CLOCK POS. SOON THEREAFTER; ATC ISSUED A TFC ALERT FOR AN ACFT AT '12 O'CLOCK POS; 2 MI; CO-ALT' AND RECOMMENDED A CLB IF NOT IN SIGHT. I ACQUIRED THE ACFT (A C172 OR SIMILAR); TOLD THE FO I HAD IT IN SIGHT AND WAS CLBING TO AVOID IT. I INITIATED A CLB TO 3500 FT MSL AND THEN ATC DIRECTED A TURN TO 010 DEGS TO INTERCEPT. DURING THE TURN WE CROSSED DIRECTLY OVER THE ACFT. THE FO EVENTUALLY GOT THE ACFT IN SIGHT AND INDICATED TO ME THAT IT WAS TURNING BACK TOWARDS US AFTER WE HAD FLOWN OVER HIM. PER THE FO'S COMMENTS THAT IT WAS EVENTUALLY SAFE TO BEGIN A DSCNT; I STARTED DOWN; INTERCEPTED FINAL AND CONTINUED THE APCH WITHOUT FURTHER INCIDENT. THE TCAS SYS HAD GIVEN US A TA; BUT NO RA. APPARENTLY WE INITIATED THE CLB BEFORE IT DECIDED TO ISSUE AN RA. THIS IS THE SECOND TIME THIS TYPE OF INCIDENT HAS OCCURRED IN THE SHORT TIME SINCE I HAVE BEEN A CAPT AT COMPANY (UPGRADED ALMOST 1 YR AGO). HERE IS THE BOTTOM LINE. THERE IS GOING TO BE A MIDAIR COLLISION IN CHICAGO. IT IS ONLY A QUESTION OF WHEN; NOT IF. THE CESSNA WHICH CAUSED THIS EVENT WAS OUTSIDE OF CTLED AIRSPACE AND NOT IN RADIO CONTACT WITH APCH. HE/SHE WAS PERFECTLY LEGAL TO BE THERE. THE PROB IS; LEGAL OR NOT; IT WAS STUPID. SINCE IT IS IMPOSSIBLE TO LEGISLATE COMMON SENSE; SOMETHING NEEDS TO BE DONE ABOUT ALLOWING THESE GA ACFT TO FLY WITHIN A FEW MI OF THE FINAL APCH COURSE AT THE SAME ALTS WE ARE BEING VECTORED AT. I DON'T CARE IF IT IS A VFR CORRIDOR BELOW OUR VECTORING ALTS OR A CHANGE IN MDW'S AIRSPACE; BUT SOMETHING NEEDS TO CHANGE NOW. THE FAA; AS IT HAS PROVEN TIME AND AGAIN; WILL NOT BE PROACTIVE UNTIL THERE IS A BODY COUNT. I STRONGLY RECOMMEND OUR COMPANY AND CHICAGO ATC PUSH THIS ISSUE UNTIL THE FAA REALIZES HOW ASININE THIS PRACTICE IS. SIMPLY HOPING THAT THE INEVITABLE BURNING HULK OF AN AIRPLANE DOESN'T HAVE OUR COMPANY NAME WRITTEN ON ITS TAIL WILL LEAD TO A BILLION PLUS DOLLAR MISTAKE. THE AIRSPACE AT MDW NEEDS TO CHANGE NOW! THERE IS ABSOLUTELY NO SANE REASON TO ALLOW GA VFR ACFT TO FLY RIGHT THROUGH APCH CORRIDORS AT ANY ARPT WITHOUT TALKING TO SOMEBODY. HUMAN ERROR IS THE MOST COMMON CAUSE OF ACFT ACCIDENTS TODAY. IN BOTH INCIDENTS THAT HAVE HAPPENED TO ME; IT WAS ONLY THE HUMAN FACTOR THAT SAVED A COLLISION. THIS TIME; THANKFULLY; BOTH THE CTLR AND I RECOGNIZED THE THREAT. THE FIRST TIME IT HAPPENED; THE CTLR WAS TOO BUSY TO NOTIFY ME OF THE THREAT. WHAT HAPPENS NEXT TIME WHEN BOTH THE CTLR AND THE CREW ARE TASK SATURATED?

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.