Narrative:

We were descending on the zzzzz RNAV arrival landing [runway] xxr in ZZZ; either just prior to ZZZZZ1; or just after; level at 6;000 feet. We heard the controller talking to another aircraft; aircraft Y also at 6;000 feet. That aircraft was issued a descent; but did not comply. A few moments later the controller asked if they had us in sight; and told aircraft Y to descend immediately; and if they did not see us; to also turn immediately. This is about the time we received the TA; and saw them ahead of us and at our altitude; on TCAS; then we received the RA; I executed the TCAS escape maneuver; TCAS issued a very steep climb; close to 6;000 ft/min. The aircraft passed beneath us at 150-200 feet. I would call this one a near miss.I'm not certain whether the controller lost situational awareness with this GA aircraft; or whether the pilot of that aircraft was not properly following instruction; or possibly both. We were at our last assigned altitude; on the arrival in level flight.the controller appeared to be working two frequencies; and seemed task saturated. Again; I'm not sure whether the controller lost sight of the situation; or whether this extreme RA was due to the GA pilot not following controller instructions.

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Original NASA ASRS Text

Title: First Officer reported a near miss during approach with GA traffic.

Narrative: We were descending on the ZZZZZ RNAV arrival landing [Runway] XXR in ZZZ; either just prior to ZZZZZ1; or just after; level at 6;000 feet. We heard the Controller talking to another aircraft; Aircraft Y also at 6;000 feet. That aircraft was issued a descent; but did not comply. A few moments later the Controller asked if they had us in sight; and told Aircraft Y to descend immediately; and if they did not see us; to also turn immediately. This is about the time we received the TA; and saw them ahead of us and at our altitude; on TCAS; then we received the RA; I executed the TCAS escape maneuver; TCAS issued a very steep climb; close to 6;000 FT/min. The aircraft passed beneath us at 150-200 feet. I would call this one a near miss.I'm not certain whether the Controller lost situational awareness with this GA aircraft; or whether the pilot of that aircraft was not properly following instruction; or possibly both. We were at our last assigned altitude; on the arrival in level flight.The Controller appeared to be working two frequencies; and seemed task saturated. Again; I'm not sure whether the Controller lost sight of the situation; or whether this extreme RA was due to the GA pilot not following Controller instructions.

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.