Regional Jet 200 ER/LR (CRJ200)
Flight Crew Air Transport Pilot (ATP)
Situational Awareness
ATC Issue All Types; Conflict Airborne Conflict
Flight Crew Took Evasive Action
Human Factors
While in the descent phase of an arrival into CHA we respond to a TCAS RA. We were operating in daytime visual conditions and given a vector by CHA approach control: HDG 310 and a descent to 6000 ft. We read back and complied with the instructions. While descending the controller amended the altitude and instructed us to maintain 7000 ft. We read back and complied with the instruction. Shortly thereafter we leveled at and maintained 7000 ft. While level at 7000 ft traffic was pointed out by ATC and reported to be at 11 o'clock and 7 miles. We visually acquired the traffic and reported in sight. Our airspeed at this time was 250 knots. Approximately 20 seconds later we received a TCAS RA and complied with the instruction to 'descend'. Prior to the RA it was visually evident that our current heading of 310 degrees and the approximate heading of 080 degrees of the aircraft would place us on a direct intercept course. We had already began preparing for evasive action when the initial TCAS TA alerted and indicated the aircraft was 400 ft below our altitude and climbing. Within 2 seconds the TCAS RA initiated and instructed the descent which we had already began preparing for. A relatively aggressive descent was required to visually avoid the traffic and comply with the RA. Initially the RA specified a 2.2 descent rate on the VSI. Even with the aggressive power reduction and downward pitch moment; the RA quickly changed to 'increase descent rate'. We continued to comply with the RA; and advised ATC that we were descending in compliance with a RA. The controller then issued a further descent to 3000 ft.
It appears to have been an issue of a VFR aircraft having received discretion in his VFR altitude and he climbed directly through our altitude as he crossed in front of us.
CRJ-200 flight crew reported responding to a RA on descent into CHA.