Narrative:

Mostly clear skies and visibility 10 SM or greater. Ca pilot flying; first officer pilot monitoring. Dtw was doing simultaneous approaches to both 4L and 3R. Cleared visual approach to 4L dtw backed up with ILS Z 4L procedure. On speed and on profile. Ap engaged. TA alert just inside natiy. Traffic was a 737 at our 10 o'clock position; approximately 700 feet below and 2.5 miles. Traffic threat was rapidly closing on our position while in a left banking turn attempting to merge onto the 4L localizer. Traffic was not on our frequency and came as a complete surprise. We were not informed by ATC of this traffic; nor were we informed that this 737 would be attempting to cut in front of us for runway 4L. The 737's closure rate and rapidly increasing proximity prompted the ca to immediately disconnect the ap and begin a turn away from the rapidly emerging threat. 1-3 seconds after the ap was disconnected we received ATC instructions to turn right heading 070 to avoid traffic. We complied. However; this assigned heading immediately put us in a position where our flight path cut across the approach path of runway 3R. Thankfully there was no traffic on approach to 3R at that time. We were given new vectors and altitudes back towards 4L where we resumed a normal; stabilized approach and landing. The 737 was sidestepped over to 4R and landed uneventfully.I am personally witnessing what I can only describe as increased preferential treatment towards airlines by approach and tower controllers throughout the united states. Controllers are vectoring flights so that they can jump ahead in line to approach and land. What I witnessed in dtw was; by far; the clearest evidence of this favoring. There has to be some type of motivator that is driving individual ATC controllers to behave this way. Why else would they do so? Why did this particular detroit controller attempt to push this flight into a bad position which comprised our safety? What was his/her motivation to do so? This event occurred on a afternoon during an arrival lull into dtw. Vectoring in front of us probably saved them less than three minutes of flight time...again; why the preferential treatment?

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Original NASA ASRS Text

Title: A319 First Officer reported a B737 was vectored in front of their aircraft while on approach to Runway 4L at DTW which caused them to take evasive action.

Narrative: Mostly clear skies and visibility 10 SM or greater. CA Pilot Flying; FO Pilot Monitoring. DTW was doing simultaneous approaches to both 4L and 3R. Cleared Visual Approach to 4L DTW backed up with ILS Z 4L procedure. On speed and on profile. AP engaged. TA alert just inside NATIY. Traffic was a 737 at our 10 o'clock position; approximately 700 feet below and 2.5 miles. Traffic threat was rapidly closing on our position while in a left banking turn attempting to merge onto the 4L Localizer. Traffic was not on our frequency and came as a complete surprise. We were not informed by ATC of this traffic; nor were we informed that this 737 would be attempting to cut in front of us for Runway 4L. The 737's closure rate and rapidly increasing proximity prompted the CA to immediately disconnect the AP and begin a turn away from the rapidly emerging threat. 1-3 seconds after the AP was disconnected we received ATC instructions to turn right heading 070 to avoid traffic. We complied. However; this assigned heading immediately put us in a position where our flight path cut across the approach path of Runway 3R. Thankfully there was no traffic on approach to 3R at that time. We were given new vectors and altitudes back towards 4L where we resumed a normal; stabilized approach and landing. The 737 was sidestepped over to 4R and landed uneventfully.I am personally witnessing what I can only describe as increased preferential treatment towards Airlines by Approach and Tower Controllers throughout the United States. Controllers are vectoring flights so that they can jump ahead in line to approach and land. What I witnessed in DTW was; by far; the clearest evidence of this favoring. There has to be some type of motivator that is driving individual ATC controllers to behave this way. Why else would they do so? Why did this particular Detroit controller attempt to push this flight into a bad position which comprised our safety? What was his/her motivation to do so? This event occurred on a afternoon during an arrival lull into DTW. Vectoring in front of us probably saved them less than three minutes of flight time...again; why the preferential treatment?

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.