Regional Jet 900 (CRJ900)
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Communication Breakdown; Situational Awareness
ATC Issue All Types; Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude
Flight Crew Took Evasive Action
Weather; Procedure; Human Factors
During our descent into ZZZ we received a TCAS RA. The CA (Captain) was PF (Pilot Flying) and I was PM (Pilot Monitoring). We were level at 3;000 feet and about 250 kts heading direct to ZZZZZ for a visual approach to Runway XX. The conditions were VMC but there was a scattered haze layer about 2;500 feet to 3;000 feet that made locating traffic difficult. During the descent we were advised of traffic at 6;000 feet and 1 o'clock we were unable to visually locate. At 3;000 feet we were advised of a second traffic aircraft by ATC. I advised ATC we saw the aircraft on TCAS but I could not visually acquire the aircraft. Our clearance was to maintain 3;000 feet and fly direct to ZZZZZ for the visual approach. Level at 3;000 feet and just outside ZZZZZ (I can't remember how far) we received a traffic alert. I was visually scanning outside to locate the traffic. Moments later I visually acquired the traffic descending now in a right hand turn toward us when we simultaneously received the RA. The RA called for a descent. The traffic aircraft had previously been 2;300 feet above us but had descended rapidly toward us then turned away in a sharp bank. The traffic aircraft was a light piston-driven twin with large tip tanks and a large nose fairing. The RA called for a descent. I called out visual sight of the traffic on the intercom and the CA advised he had sight of the traffic. The CA disconnected the autopilot and initiated a descent per the RA as well as a left turn to visually avoid the traffic. The CA later stated the RA called for between a 1;000 feet and 2;000 feet per minute descent; which at 3;000 feet MSL and 2;200 feet AGL would have descended us rapidly toward the ground. My focused during the avoidance maneuver remained outside the aircraft with visual contact on the traffic to ensure we avoided the traffic and the ground. After we cleared the traffic moments later I contacted ATC to advise them we had received a traffic RA and we were turning back to ZZZZZ. The CA returned the aircraft to 3;000 feet and asked me to reengage the autopilot. By this time we were between 5 and 7 miles from the airport. The controller confirmed we were direct back to ZZZZZ; we had a visual on the airport then cleared us for the visual approach from a left base at 3;000 feet. We were high and about 1 mile from ZZZZZ. The CA did an excellent job of recognizing we were high; slowing the aircraft early and initiating a descent to make a safe landing.The traffic aircraft had to be within the class C airspace. If not it was just outside the Class C airspace and maneuvering. The controller called out the traffic to us but I was unable to visually confirm the traffic because of a haze layer. In my communication to the controller I stated I saw the aircraft on TCAS but did not have visual of the aircraft. I think the controller must have gotten distracted between telling us about the traffic and the RA (it happened quickly). In defense of the controller the traffic aircraft must have been doing training maneuvers because he was changing altitude and heading very quickly and that probably affected the controller's ability to vector us around the traffic.  I should not have said I had the aircraft on TCAS while also saying no visual contact. I might have confused the controller. TCAS is not sufficient for VFR clearance. I should have just said negative visual contact and inquired with the controller for traffic clearance. Without visual contact the controller would have been required to vector us around the traffic if we did not have visual contact with the traffic. The controller must have missed judged our distance from the traffic. However the traffic; based on their location; should have been in controlled class C airspace and in contact with ATC.
CRJ-900 First Officer reported that miscommunication with ATC resulted in evasive action to avoid another aircraft.