Narrative:

While flying air carrier cmh-dtw, inbound on dtw 147 degree radial at 12000 ft, I was advised of VFR traffic at 10 O'clock position, 10 mi, same altitude. ZOB then advised 'traffic 11 O'clock position, 5 mi, turn left 30 degrees.' at this point I obtained visual contact with the aircraft. We appeared to be headed directly at each other. ZOB then commanded a further left turn to 270 degrees. At this point it was apparent to me that a midair collision was possible, and rather than turn belly-up to the aircraft, I elected to keep him in sight and climb 500 ft. While at 12500 ft the VFR aircraft passed directly below me at 12000 ft. The TCASII did not activate until he had passed and I was returning to my assigned altitude. Without visual sighting, this could have been a much more serious event. The ATC controller failed to recognize the seriousness of the situation in a timely manner, and when he did, he attempted to turn us into the path of the oncoming aircraft with insufficient time to avoid a collision. I felt that my radius of turn at that speed was insufficient to clear his path, so I elected to climb 500 ft. Had this situation occurred in WX or had I not seen him visually, this could have been a very serious incident. I believe the ATC controller made an incorrect attempt to separate the aircraft after waiting too long to recognize the danger. I also am curious why a VFR aircraft was flying at 12000 ft through the detroit arrival corridor.

Google
 

Original NASA ASRS Text

Title: DC9 FLC INITIATE AN EVASIVE CLB IN LIEU OF VECTORS DUE TO ZOB ISSUED TFC. PIC QUESTIONS CTLR HDGS TO CLR TFC.

Narrative: WHILE FLYING ACR CMH-DTW, INBOUND ON DTW 147 DEG RADIAL AT 12000 FT, I WAS ADVISED OF VFR TFC AT 10 O'CLOCK POS, 10 MI, SAME ALT. ZOB THEN ADVISED 'TFC 11 O'CLOCK POS, 5 MI, TURN L 30 DEGS.' AT THIS POINT I OBTAINED VISUAL CONTACT WITH THE ACFT. WE APPEARED TO BE HEADED DIRECTLY AT EACH OTHER. ZOB THEN COMMANDED A FURTHER L TURN TO 270 DEGS. AT THIS POINT IT WAS APPARENT TO ME THAT A MIDAIR COLLISION WAS POSSIBLE, AND RATHER THAN TURN BELLY-UP TO THE ACFT, I ELECTED TO KEEP HIM IN SIGHT AND CLB 500 FT. WHILE AT 12500 FT THE VFR ACFT PASSED DIRECTLY BELOW ME AT 12000 FT. THE TCASII DID NOT ACTIVATE UNTIL HE HAD PASSED AND I WAS RETURNING TO MY ASSIGNED ALT. WITHOUT VISUAL SIGHTING, THIS COULD HAVE BEEN A MUCH MORE SERIOUS EVENT. THE ATC CTLR FAILED TO RECOGNIZE THE SERIOUSNESS OF THE SIT IN A TIMELY MANNER, AND WHEN HE DID, HE ATTEMPTED TO TURN US INTO THE PATH OF THE ONCOMING ACFT WITH INSUFFICIENT TIME TO AVOID A COLLISION. I FELT THAT MY RADIUS OF TURN AT THAT SPD WAS INSUFFICIENT TO CLR HIS PATH, SO I ELECTED TO CLB 500 FT. HAD THIS SIT OCCURRED IN WX OR HAD I NOT SEEN HIM VISUALLY, THIS COULD HAVE BEEN A VERY SERIOUS INCIDENT. I BELIEVE THE ATC CTLR MADE AN INCORRECT ATTEMPT TO SEPARATE THE ACFT AFTER WAITING TOO LONG TO RECOGNIZE THE DANGER. I ALSO AM CURIOUS WHY A VFR ACFT WAS FLYING AT 12000 FT THROUGH THE DETROIT ARR CORRIDOR.

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.