Medium large transport on vectored approach has TCASII RA. Responds.

Attributes
ACN	251768
Time
Date	199309
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : bwi
State Reference	MD
Altitude	msl bound lower : 3500 msl bound upper : 4000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : bwi
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent : approach
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 240 flight time total : 11000
ASRS Report	251768
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 70 flight time total : 8000 flight time type : 3500
ASRS Report	252786
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : took evasive action
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

While on right base about 10 mi from bwi at 4000 ft, being vectored for ILS runway 33L, TCASII issued a TA, then an RA. I looked for the traffic in the early morning haze, did not see it, descended to 3500 ft to comply with the RA. ATC said it must have been the aircraft we were going to follow (turning a left base for the same ILS course, 3 1/2 mi ahead of us). The system worked well and we were cleared for the approach from 3500 ft. No traffic conflicts. Normal approach and landing.

Original NASA ASRS Text

Title: MLG ON VECTORED APCH HAS TCASII RA. RESPONDS.

Narrative: WHILE ON R BASE ABOUT 10 MI FROM BWI AT 4000 FT, BEING VECTORED FOR ILS RWY 33L, TCASII ISSUED A TA, THEN AN RA. I LOOKED FOR THE TFC IN THE EARLY MORNING HAZE, DID NOT SEE IT, DSNDED TO 3500 FT TO COMPLY WITH THE RA. ATC SAID IT MUST HAVE BEEN THE ACFT WE WERE GOING TO FOLLOW (TURNING A L BASE FOR THE SAME ILS COURSE, 3 1/2 MI AHEAD OF US). THE SYS WORKED WELL AND WE WERE CLRED FOR THE APCH FROM 3500 FT. NO TFC CONFLICTS. NORMAL APCH AND LNDG.

Data retrieved from NASA's ASRS site as of July 2007 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.