Large Transport; Low Wing; 2 Turbojet Eng
Communication Breakdown; Confusion; Workload
ATC Issue All Types; Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude
Flight Crew Became Reoriented; Flight Crew Returned To Clearance; Flight Crew Took Evasive Action
Airspace Structure; Environment - Non Weather Related; Procedure
On a right base approaching from the south for Runway 10 at 4;000 FT MSL; Potomac Approach called traffic to follow at two o'clock for the visual to Runway 10. The Captain; PM; responded; 'I have traffic at one o'clock at our altitude. Is that our traffic? Approach responded; 'Follow him. Cleared the visual Runway 10.' This traffic was on a left base from the north. Expecting our traffic to start his turn to final so we could follow; we maintained our last assigned heading and altitude. Just as we were about to query ATC; we received a Traffic Alert (TA) so began a descending turn to final. This was quickly followed by a RA. We complied with the RA (a descent) and heard the other aircraft say over the radio that they were responding to a RA. After receiving a 'clear of conflict;' we continued the approach and landing. I do not recall ATC requesting a call at any time after this event.
An air carrier on a visual approach to BWI Runway 10 took evasive action to a TCAS RA from unknown traffic as they were about to turn base from the south.