EMB ERJ 170/175 ER/LR
Flight Crew Air Transport Pilot (ATP)
ATC Issue All Types; Conflict Airborne Conflict
Flight Crew Took Evasive Action
Procedure; Human Factors
Approximately one mile outside the marker for Runway 10 in ORD we received a TCAS traffic alert. The aircraft appeared to be 700 FT below. We started looking for traffic and at no point did ORD Tower say anything to us about traffic. The target began to get closer and closer to us and when we did spot the aircraft it was at our same altitude in a right hand bank directly towards us. It was close enough we could see in the windscreen of this C172 or C152 aircraft; and we did receive a RA and reacted accordingly. Advised Tower; after the RA was over we continued and landed without further incident.
ERJ-170 First Officer reported RA-level airborne conflict on ORD arrival with no traffic call from Tower.