TCASII RA. Air carrier descends.

Attributes
ACN	183959
Time
Date	199107
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : buf
State Reference	NY
Altitude	msl bound lower : 5400 msl bound upper : 6000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent : approach descent other
Route In Use	enroute : on vectors enroute airway : bufr
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 180 flight time total : 12500 flight time type : 7500
ASRS Report	183959
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial pilot : flight engineer
Experience	flight time last 90 days : 200 flight time total : 13000 flight time type : 200
ASRS Report	184112
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : took evasive action
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 12000 vertical : 0
Supplementary
Primary Problem	Ambiguous
Air Traffic Incident	Pilot Deviation

Narrative:

Inbound to the buf airport, we had been turned over to approach control, on radar vectors, heading 055 degree at 6000 ft MSL. We received a TCAS 'traffic' alert, with intruder showing at 2 O'clock, 2 1/2-3 mi. As we scanned the area visually, we received a resolution advisory, 'descend', with intruder showing at 2 O'clock, 2 mi, 0 relative altitude (level with us). We began a descent from our assigned altitude of 6000 ft MSL at a rate of 1500-2000 FPM. Approach control was immediately advised of our descent and reason for leaving our assigned altitude. This contact was made within 200-300 ft of leaving 6000 ft. Approach control acknowledged and cleared us immediately down to 2500 ft MSL, with the comment that our traffic we were descending to avoid 'had us in sight'. We never saw the traffic. TCAS alert then instructed to 'monitor vertical speed' and subsequently 'clear of traffic'. Normal landing was accomplished after which I contacted the tower supervisor, advising him of the event. Company flight control was also notified.

Original NASA ASRS Text

Title: TCASII RA. ACR DSNDS.

Narrative: INBOUND TO THE BUF ARPT, WE HAD BEEN TURNED OVER TO APCH CTL, ON RADAR VECTORS, HDG 055 DEG AT 6000 FT MSL. WE RECEIVED A TCAS 'TFC' ALERT, WITH INTRUDER SHOWING AT 2 O'CLOCK, 2 1/2-3 MI. AS WE SCANNED THE AREA VISUALLY, WE RECEIVED A RESOLUTION ADVISORY, 'DSND', WITH INTRUDER SHOWING AT 2 O'CLOCK, 2 MI, 0 RELATIVE ALT (LEVEL WITH US). WE BEGAN A DSCNT FROM OUR ASSIGNED ALT OF 6000 FT MSL AT A RATE OF 1500-2000 FPM. APCH CTL WAS IMMEDIATELY ADVISED OF OUR DSCNT AND REASON FOR LEAVING OUR ASSIGNED ALT. THIS CONTACT WAS MADE WITHIN 200-300 FT OF LEAVING 6000 FT. APCH CTL ACKNOWLEDGED AND CLRED US IMMEDIATELY DOWN TO 2500 FT MSL, WITH THE COMMENT THAT OUR TFC WE WERE DSNDING TO AVOID 'HAD US IN SIGHT'. WE NEVER SAW THE TFC. TCAS ALERT THEN INSTRUCTED TO 'MONITOR VERT SPD' AND SUBSEQUENTLY 'CLR OF TFC'. NORMAL LNDG WAS ACCOMPLISHED AFTER WHICH I CONTACTED THE TWR SUPVR, ADVISING HIM OF THE EVENT. COMPANY FLT CTL WAS ALSO NOTIFIED.

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.