An air carrier on a visual approach to bwi runway 10 took evasive action to a TCAS RA from unknown t...

Narrative:

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.

Original NASA ASRS Text

Title: 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.

Narrative: 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.

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.

Attributes
ACN	1110602
Time
Date	201308
Local Time Of Day	1801-2400
Place
Locale Reference	BWI.Airport
State Reference	MD
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Make Model Name	Large Transport Low Wing 2 Turbojet Eng
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Route In Use	Visual Approach
Flight Plan	IFR
Person 1
Function	First Officer Pilot Flying
Events
Anomaly	ATC Issue All Types Conflict Airborne Conflict Deviation - Altitude Excursion From Assigned Altitude

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.