Narrative:

Approaching the sailz waypoint; our assigned altitude was 3500 feet due to previous conflicting traffic at 2500 feet prior to turning inbound to sailz. As we approached sailz; the FMS was tracking LNAV towards sailz; our altitude was 3500 feet and we were given a traffic call that VFR traffic was at 3000 feet at our 12 o'clock. At approximately 1.5 miles prior to sailz; the controller instructed us to turn 20 degrees right due to the traffic. I believe our aircraft had just completed rolling out; so it seemed as though the pilot flying had indeed dialed in 20 degrees to the right. I failed to monitor heading select and we were still in LNAV directly towards sailz when we should have been turning to the right of sailz according to the instruction. At the time the controller instructed us to expedite our turn; we received an RA due to the traffic at sailz; which was climbing to 3200 feet as we maintained level 3500 feet. We followed the RA guidance and quickly cleared the conflict. Additional distractions that contributed to the RA were: ATC radio congestion which distracted both pilots from following immediate instructions from ATC and confusion as to why other aircraft were conflicting our approach to land under IFR handling; despite the VMC day.I believe that VFR traffic should not be allowed to transit an IFR corridor at the same altitude as the inbound traffic to land. This poses a significant threat to commercial aviation and could result in a midair collision; clearly an unacceptable outcome for something that can be avoided.

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Original NASA ASRS Text

Title: B737-800 First Officer reported a track deviation resulted in an airborne conflict during approach into MDW.

Narrative: Approaching the SAILZ waypoint; our assigned altitude was 3500 feet due to previous conflicting traffic at 2500 feet prior to turning inbound to SAILZ. As we approached SAILZ; the FMS was tracking LNAV towards SAILZ; our altitude was 3500 feet and we were given a traffic call that VFR traffic was at 3000 feet at our 12 o'clock. At approximately 1.5 miles prior to SAILZ; the Controller instructed us to turn 20 degrees right due to the traffic. I believe our aircraft had just completed rolling out; so it seemed as though the Pilot Flying had indeed dialed in 20 degrees to the right. I failed to monitor heading select and we were still in LNAV directly towards SAILZ when we should have been turning to the right of SAILZ according to the instruction. At the time the Controller instructed us to expedite our turn; we received an RA due to the traffic at SAILZ; which was climbing to 3200 feet as we maintained level 3500 feet. We followed the RA guidance and quickly cleared the conflict. Additional distractions that contributed to the RA were: ATC radio congestion which distracted both pilots from following immediate instructions from ATC and confusion as to why other aircraft were conflicting our approach to land under IFR handling; despite the VMC day.I believe that VFR traffic should not be allowed to transit an IFR corridor at the same altitude as the inbound traffic to land. This poses a significant threat to commercial aviation and could result in a midair collision; clearly an unacceptable outcome for something that can be avoided.

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.