Do 328 TJ (Turbojet)
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Flight Crew Last 90 Days 125; Flight Crew Total 5700; Flight Crew Type 3000
Conflict NMAC
Flight Crew Took Evasive Action
Airspace Structure; Human Factors; Procedure
VMC on an IFR flight plan talking to Chicago Center; 20 NM southwest of DPA level at 4;000 FT shortly after being cleared direct DPA (was previously direct JOT). Level at 4;000 FT the TCAS in 'below' mode started painting a target approximately 3 miles at 12:00 500 FT below; followed very quickly by a TA 'Traffic; Traffic' announcement. Both my First Officer and I immediately acknowledged the alert. Chicago Center Controller also simultaneously alerted us to 'VFR traffic 3 miles and 12:00; 500 FT below'. Both I and the First Officer started scanning outside to identify the threat. We did not make visual contact with the traffic. We then received a TCAS RA of 'Climb; Climb'. I immediately advanced the power levers to maximum thrust and followed the RA climb command. We never identified the VFR traffic. I leveled at 4;500 FT. We reported the RA to ATC and were then cleared to descend to 4;000 FT.
Do328 Captain; at 4;000 FT southwest of DPA; experiences a TCAS RA with VFR traffic at 3;500 FT and takes evasive action.