TCASII causes medium large transport to descend to avoid conflicting traffic.

Attributes
ACN	243600
Time
Date	199306
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : bwi
State Reference	MD
Altitude	msl bound lower : 2500 msl bound upper : 3000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : bwi artcc : zdc
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	cruise other
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : commercial pilot : flight engineer pilot : instrument pilot : atp
Experience	flight time last 90 days : 100 flight time total : 8500 flight time type : 4000
ASRS Report	243600
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	conflict : airborne less severe non adherence other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other controllera
Resolutory Action	flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 6000 vertical : 1000
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	other

Narrative:

While being vectored to final approach for runway 33L at bwi, received TCASII RA 'descend.' departed 3000 ft assigned altitude for 2500 ft when controller (who was unable to get in a word on frequency due to heavy traffic) called out traffic to us at '10-11 O'clock less than a mi descend to 2000 ft.' we were already in the descent as the controller spoke and 'clear of conflict' advisory came from the TCASII as we passed 2500 ft on the descent. Without TCASII our traffic conflict would have been closer but approach control's call would have been in time to prevent a collision.

Original NASA ASRS Text

Title: TCASII CAUSES MLG TO DSND TO AVOID CONFLICTING TFC.

Narrative: WHILE BEING VECTORED TO FINAL APCH FOR RWY 33L AT BWI, RECEIVED TCASII RA 'DSND.' DEPARTED 3000 FT ASSIGNED ALT FOR 2500 FT WHEN CTLR (WHO WAS UNABLE TO GET IN A WORD ON FREQ DUE TO HVY TFC) CALLED OUT TFC TO US AT '10-11 O'CLOCK LESS THAN A MI DSND TO 2000 FT.' WE WERE ALREADY IN THE DSCNT AS THE CTLR SPOKE AND 'CLR OF CONFLICT' ADVISORY CAME FROM THE TCASII AS WE PASSED 2500 FT ON THE DSCNT. WITHOUT TCASII OUR TFC CONFLICT WOULD HAVE BEEN CLOSER BUT APCH CTL'S CALL WOULD HAVE BEEN IN TIME TO PREVENT A COLLISION.

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.