Narrative:

We were VFR northbound at 8500' crossing the top of the chicago TCA. I reached behind my seat to put away a chart and heard a short, loud woosh, like the sound of a door coming open in flight. I turned back immediately and asked my wife (in the right seat) if she saw anything. She said an small transport, blue and white, went under the right wing. After discussing it with her further I estimated the distance at 300-500' below us and about 300' to our right. It had to be close to hear its engines in the cabin of our plane. We continued northbound to the northern edge of the TCA just north of waukegan, il, and descended to 2500' VFR and continued onto ues, our destination. Since I see this type of situation from both the viewpoint of the small aircraft owner and operator and as a heavy transport captain, I have mixed feelings on what should be done. I agree that small aircraft's should all be required to have a transponder with mode C and that the TCA's should be extended to 12500' or the positive control area lowered to 10000' and TCA's raised to 10000'. But if small aircraft's are to be required to carry basically the same equipment as the average airliner, they should no longer be treated as second class citizens in busy airspace. There should be more corridors through TCA's, even if they require a controller to monitor the traffic through them and ATC services provided to all traffic on a first come first serve basis for VFR traffic as well. I realize the latter would mean a lot more controller workload and is basically impossible right now. Lastly, I would recommend that all aircraft equipped with transponder west/O mode C should be required to set the last digit of their transponders to match the altitude they are flying at. Example--cruising at 3000' MSL enter 1203, or 7500' MSL enter 7 or 11500' MSL enter 1211. It would only require 12 of the 4096 codes on the transponder and give controllers an instant 'poor man's' encoder. Our return flight, by the way, was on an IFR flight plan on a route from milwaukee to louisville via rockford, il. I've had enough of the chicago TCA when flying VFR.

Related reports:

Google
 

Original NASA ASRS Text

Title: NMAC BETWEEN GA-SMA AND UNK-SMT.

Narrative: WE WERE VFR NBOUND AT 8500' XING THE TOP OF THE CHICAGO TCA. I REACHED BEHIND MY SEAT TO PUT AWAY A CHART AND HEARD A SHORT, LOUD WOOSH, LIKE THE SOUND OF A DOOR COMING OPEN IN FLT. I TURNED BACK IMMEDIATELY AND ASKED MY WIFE (IN THE RIGHT SEAT) IF SHE SAW ANYTHING. SHE SAID AN SMT, BLUE AND WHITE, WENT UNDER THE RIGHT WING. AFTER DISCUSSING IT WITH HER FURTHER I ESTIMATED THE DISTANCE AT 300-500' BELOW US AND ABOUT 300' TO OUR RIGHT. IT HAD TO BE CLOSE TO HEAR ITS ENGS IN THE CABIN OF OUR PLANE. WE CONTINUED NBOUND TO THE NORTHERN EDGE OF THE TCA JUST N OF WAUKEGAN, IL, AND DSNDED TO 2500' VFR AND CONTINUED ONTO UES, OUR DEST. SINCE I SEE THIS TYPE OF SITUATION FROM BOTH THE VIEWPOINT OF THE SMA OWNER AND OPERATOR AND AS A HVT CAPT, I HAVE MIXED FEELINGS ON WHAT SHOULD BE DONE. I AGREE THAT SMA'S SHOULD ALL BE REQUIRED TO HAVE A TRANSPONDER WITH MODE C AND THAT THE TCA'S SHOULD BE EXTENDED TO 12500' OR THE PCA LOWERED TO 10000' AND TCA'S RAISED TO 10000'. BUT IF SMA'S ARE TO BE REQUIRED TO CARRY BASICALLY THE SAME EQUIP AS THE AVERAGE AIRLINER, THEY SHOULD NO LONGER BE TREATED AS SECOND CLASS CITIZENS IN BUSY AIRSPACE. THERE SHOULD BE MORE CORRIDORS THROUGH TCA'S, EVEN IF THEY REQUIRE A CTLR TO MONITOR THE TFC THROUGH THEM AND ATC SVCS PROVIDED TO ALL TFC ON A FIRST COME FIRST SERVE BASIS FOR VFR TFC AS WELL. I REALIZE THE LATTER WOULD MEAN A LOT MORE CTLR WORKLOAD AND IS BASICALLY IMPOSSIBLE RIGHT NOW. LASTLY, I WOULD RECOMMEND THAT ALL ACFT EQUIPPED WITH TRANSPONDER W/O MODE C SHOULD BE REQUIRED TO SET THE LAST DIGIT OF THEIR TRANSPONDERS TO MATCH THE ALT THEY ARE FLYING AT. EXAMPLE--CRUISING AT 3000' MSL ENTER 1203, OR 7500' MSL ENTER 7 OR 11500' MSL ENTER 1211. IT WOULD ONLY REQUIRE 12 OF THE 4096 CODES ON THE TRANSPONDER AND GIVE CTLRS AN INSTANT 'POOR MAN'S' ENCODER. OUR RETURN FLT, BY THE WAY, WAS ON AN IFR FLT PLAN ON A ROUTE FROM MILWAUKEE TO LOUISVILLE VIA ROCKFORD, IL. I'VE HAD ENOUGH OF THE CHICAGO TCA WHEN FLYING VFR.

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.