Regional Jet 200 ER/LR (CRJ200)
Flight Crew Air Transport Pilot (ATP)
Communication Breakdown
Conflict Airborne Conflict
Flight Crew FLC complied w / Automation / Advisory; Flight Crew Returned To Clearance; Flight Crew Took Evasive Action
Airspace Structure
On arrival into ABE; was on vector and assigned altitude of 4;000 FT. Had cyan target on TCAS at 1 to 2 o'clock that appeared to be moving toward our flight path. The FO and I were attempting to visually acquire the traffic when we received an amber TA. I did not have the visual on traffic; but checking the TCAS display he appeared to be in closer than one mile and closing. I told the First Officer to prepare to climb. I was about to ask Approach about him as we had not been advised of this traffic when the TCAS indicated the target had began to climb and was now indicating less than 400 FT of vertical separation. TCAS RA climb activated and we immediately began climbing. We deviated from our assigned altitude by 2;000 FT climbing to 6;000 before receiving clear of conflict. ATC was advised of the RA and we were cleared to return to our previously assigned altitude. After completing the maneuver and re leveling at 4;000; I asked what the story was on the airplane that had caused it and it was a VFR aircraft that had not maintained his altitude.The threat is separating IFR and VFR traffic by 500 FT in the terminal area. I know it's legal but this is not the first time this has caused me to have an RA. We were flying on an assigned vector and altitude. This one happened pretty quick but I should have been a little quicker to request information on the unknown target and possibly a climb or turn before the RA. In this case there was very little time to take action aside from prompt compliance with the RA.
ATC told us the GA aircraft that caused the event was climbing to the wrong altitude.
A CRJ-200 flight crew responded to a TCAS RA with respect to a VFR GA aircraft which intruded on the minimum 500 foot vertical separation requirement climbing toward the CRJ.