ERJ 145 crew reported a NMAC after receiving an RA while in congested airspace.
Synopsis
ERJ 145 crew reported a NMAC after receiving an RA while in congested airspace.
Narrative
I was on the ZZZZZ arrival flying from ZZZ1 to ZZZ. ATC assigned us to hold at ZZZZZ (West as published at 18000 ft.) because they were changing the landing direction from North to South in ZZZ. During our first turn in the hold (on our outbound leg) ATC instructed us to turn left direct to ZZZZZ1 and descend to 13000 ft. During our turn to ZZZZZ1 we received a TA/RA to climb. I was Pilot flying (PF); saw the aircraft traffic conflict visually in the opposite direction approximately 100 ft. below and within 500 ft. laterally. I saw the TCAS display showing us within 100 ft. and I clicked off the autopilot and complied with the climb RA. We climbed aggressively up to 16600 ft. at which point the Captain (CA) advised ATC of the RA and that we were now at 16000 ft. and PM asked what altitude ATC wanted us to climb or descend to. ATCs next instructions to us were to maintain 16000 and proceed direct ZZZZZ1. While continuing our left turn to ZZZZZ1 we received a second TA (just a TA this time; no RA) for the same aircraft. This is the second time I saw the aircraft visually and it was 10 o' clock high approximately 2 miles and approximately 1000 above us (by my visual estimation). I was still hand flying so the CA told me to continue to avoid the aircraft so we turned right and descended with the intent to create more separation and avoid another RA.
Second reporter narrative
[Narrative contained no additional information.]
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.