EMB170 flight crew has TCAS RA during mount vernon arrival to dca.

Attributes
ACN	697772
Time
Date	200605
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : dca.airport
State Reference	DC
Altitude	msl single value : 4000
Environment
Flight Conditions	VMC
Aircraft 1
Controlling Facilities	tracon : dca.tracon
Operator	common carrier : air carrier
Make Model Name	EMB ERJ 170/175 ER&LR
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : approach
Route In Use	approach : charted visual
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 100 flight time total : 4500 flight time type : 750
ASRS Report	697772
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : nmac non adherence : required legal separation
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : took evasive action
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 0 vertical : 200
Supplementary
Problem Areas	Flight Crew Human Performance ATC Human Performance Airspace Structure
Primary Problem	Ambiguous

Narrative:

On vector for mount vernon visual at 4000 ft sbound; approach called traffic at 1 O'clock position; 3500 ft. Traffic not visually acquired but displayed on TCAS. Aircraft passed under us with 500 ft separation. Immediately after passing we were given a turn to 090 degrees. Out of turn; we received the RA with 200 ft separation from same aircraft. We took evasive action and climbed 300 ft. ATC was notified of RA. Unsure of VFR traffic's flight path; estimate aircraft must have been in right turn in which they climbed 300 ft; in order to pass underneath us. Unsure if other aircraft had clearance to be in class B airspace.

Original NASA ASRS Text

Title: EMB170 FLT CREW HAS TCAS RA DURING MOUNT VERNON ARR TO DCA.

Narrative: ON VECTOR FOR MOUNT VERNON VISUAL AT 4000 FT SBOUND; APCH CALLED TFC AT 1 O'CLOCK POS; 3500 FT. TFC NOT VISUALLY ACQUIRED BUT DISPLAYED ON TCAS. ACFT PASSED UNDER US WITH 500 FT SEPARATION. IMMEDIATELY AFTER PASSING WE WERE GIVEN A TURN TO 090 DEGS. OUT OF TURN; WE RECEIVED THE RA WITH 200 FT SEPARATION FROM SAME ACFT. WE TOOK EVASIVE ACTION AND CLBED 300 FT. ATC WAS NOTIFIED OF RA. UNSURE OF VFR TFC'S FLT PATH; ESTIMATE ACFT MUST HAVE BEEN IN R TURN IN WHICH THEY CLBED 300 FT; IN ORDER TO PASS UNDERNEATH US. UNSURE IF OTHER ACFT HAD CLRNC TO BE IN CLASS B AIRSPACE.

Data retrieved from NASA's ASRS site as of January 2009 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.