Narrative:

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.

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Original NASA ASRS Text

Title: Do328 Captain; at 4;000 FT southwest of DPA; experiences a TCAS RA with VFR traffic at 3;500 FT and takes evasive action.

Narrative: 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.

Data retrieved from NASA's ASRS site as of July 2013 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.