Narrative:

During our arrival into ZZZ we encountered a traffic event with another aircraft that was not in communication with ATC. As pilot flying we were on the ZZZZZ5 arrival [VOR] transition landing runway [xx]. We were cleared direct zzzzz and to cross it at 6000 [ft]. We started our descent from 11000 ft and were descending at 1500 FPM 250 KTS; our track to zzzzz was 180 degrees. We completed the approach checklist shortly after crossing 10000 ft and shortly after ATC instructed to increase descent through 7000 ft as they reported traffic at 1 to 2 o' clock climbing to 7000 ft. I deployed spoilers and increased descent rate to 2500 FPM. The traffic appeared on our TCAS mfd display as we continued descent. It appeared the lateral distance continued to close and as we noticed; ATC cleared us 20 degrees to the left. During this turn we received two yellow TCAS caution alerts. Shortly after we descended through 7000 ft; I made visual contact with the traffic and the TCAS cautions stopped. The other aircraft appeared fairly distant and appeared level at 7000 ft (we had leveled off at 6000 ft by this point in time). Right after this; ATC cleared us for a left turn to 110 degrees and to descend to 5000 ft to remain clear of traffic. After we established the turn and descent I looked back to maintain visual contact with the other aircraft and saw that it had closed both lateral and vertical distance significantly and was continuing to close. At this point I remember disconnecting the autopilot and accelerated the turn to avoid the other aircraft. As I did this we received the first of two TCAS ras. I complied with the RA and continued the turn to 110 degrees as the other aircraft was so close it appeared as if it was lining up for a parallel precision runway monitoring (prm) approach. I lost sight of it so as to fly the a/c and comply with the RA (2000 fpm descent). ATC cleared us to descend to 3000 ft. Shortly after we cleared the first TCAS RA and stabilized the a/c we received a second RA that called for a continued descent; I complied. The traffic was passing over us at this point and was visible on the TCAS mfd display. We continued the descent per the RA and it appeared as if the other a/c was continuing a descent toward us; per the TCAS mfd. Its target showed that its vertical distance was decreasing; coming as close as 300 feet above us. I had to increase the descent rate to as high as 2700 FPM to gain separation again and clear the RA. Shortly after the second RA was cleared and assumed normal control of the a/c. We leveled at 3000ft; re-engaged the autopilot for the rest of the arrival and completed the flight without further incident.

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Original NASA ASRS Text

Title: CRJ-900 First Officer reported an aggressive TCAS escape maneuver was required to main clear of descending traffic.

Narrative: During our arrival into ZZZ we encountered a traffic event with another aircraft that was not in communication with ATC. As pilot flying we were on the ZZZZZ5 arrival [VOR] transition landing runway [XX]. We were cleared direct ZZZZZ and to cross it at 6000 [ft]. We started our descent from 11000 ft and were descending at 1500 FPM 250 KTS; our track to ZZZZZ was 180 degrees. We completed the approach checklist shortly after crossing 10000 ft and shortly after ATC instructed to increase descent through 7000 ft as they reported traffic at 1 to 2 o' clock climbing to 7000 ft. I deployed spoilers and increased descent rate to 2500 FPM. The traffic appeared on our TCAS MFD display as we continued descent. It appeared the lateral distance continued to close and as we noticed; ATC cleared us 20 degrees to the left. During this turn we received two yellow TCAS caution alerts. Shortly after we descended through 7000 ft; I made visual contact with the traffic and the TCAS cautions stopped. The other aircraft appeared fairly distant and appeared level at 7000 ft (we had leveled off at 6000 ft by this point in time). Right after this; ATC cleared us for a left turn to 110 degrees and to descend to 5000 ft to remain clear of traffic. After we established the turn and descent I looked back to maintain visual contact with the other aircraft and saw that it had closed both lateral and vertical distance significantly and was continuing to close. At this point I remember disconnecting the autopilot and accelerated the turn to avoid the other aircraft. As I did this we received the first of two TCAS RAs. I complied with the RA and continued the turn to 110 degrees as the other aircraft was so close it appeared as if it was lining up for a parallel Precision Runway Monitoring (PRM) approach. I lost sight of it so as to fly the a/c and comply with the RA (2000 fpm descent). ATC cleared us to descend to 3000 ft. Shortly after we cleared the first TCAS RA and stabilized the a/c we received a second RA that called for a continued descent; I complied. The traffic was passing over us at this point and was visible on the TCAS MFD display. We continued the descent per the RA and it appeared as if the other a/c was continuing a descent toward us; per the TCAS MFD. Its target showed that its vertical distance was decreasing; coming as close as 300 feet above us. I had to increase the descent rate to as high as 2700 FPM to gain separation again and clear the RA. Shortly after the second RA was cleared and assumed normal control of the a/c. We leveled at 3000ft; re-engaged the autopilot for the rest of the arrival and completed the flight without further incident.

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.