Air carrier flight crew receives TCAS alert while descending. Responds.

Attributes
ACN	181354
Time
Date	199106
Day	Sun
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : atl
State Reference	GA
Altitude	msl bound lower : 11000 msl bound upper : 11400
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : atl artcc : dca
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : cfi pilot : atp pilot : commercial
Experience	flight time last 90 days : 150 flight time total : 5000 flight time type : 1000
ASRS Report	181354
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 8000 flight time type : 1500
ASRS Report	181361
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : clearance other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : took evasive action flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

While descending to 11000', we received a TA. I looked at display to see where traffic was, then visually acquired traffic outside. As I was watching the traffic maybe 5-10 seconds, we received an RA climb command. Captain immediately began a climb. As we received the clear of conflict command, the altitude alert went off. We were 11400-11500'. Atl verified that we were leveling at 11000'. We acknowledged that we were. The problem was, we were descending while the other aircraft was climbing and the TCAS didn't know what altitudes the aircraft were to level off at. It began the warning commands and we were distracted by them and ended up deviating from altitude when there was really no conflict. We were in a descent to 11000'; other aircraft was in a climb to 10000'. Supplemental information from acn 181361: the frequent, too loud and distracting TCAS 'traffic, traffic' warnings I have heard over the past several months have made me somewhat less than a true fan of the system. The distraction factor may have played a roll in this incident, but if you throw out all the shoulda's and coulda's, the bottom line is that the TCAS saved my bacon on this one. I'll reassess my thinking on TCAS.

Original NASA ASRS Text

Title: ACR FLT CREW RECEIVES TCAS ALERT WHILE DESCENDING. RESPONDS.

Narrative: WHILE DSNDING TO 11000', WE RECEIVED A TA. I LOOKED AT DISPLAY TO SEE WHERE TFC WAS, THEN VISUALLY ACQUIRED TFC OUTSIDE. AS I WAS WATCHING THE TFC MAYBE 5-10 SECS, WE RECEIVED AN RA CLB COMMAND. CAPT IMMEDIATELY BEGAN A CLB. AS WE RECEIVED THE CLR OF CONFLICT COMMAND, THE ALT ALERT WENT OFF. WE WERE 11400-11500'. ATL VERIFIED THAT WE WERE LEVELING AT 11000'. WE ACKNOWLEDGED THAT WE WERE. THE PROB WAS, WE WERE DSNDING WHILE THE OTHER ACFT WAS CLBING AND THE TCAS DIDN'T KNOW WHAT ALTS THE ACFT WERE TO LEVEL OFF AT. IT BEGAN THE WARNING COMMANDS AND WE WERE DISTRACTED BY THEM AND ENDED UP DEVIATING FROM ALT WHEN THERE WAS REALLY NO CONFLICT. WE WERE IN A DSNT TO 11000'; OTHER ACFT WAS IN A CLB TO 10000'. SUPPLEMENTAL INFO FROM ACN 181361: THE FREQUENT, TOO LOUD AND DISTRACTING TCAS 'TFC, TFC' WARNINGS I HAVE HEARD OVER THE PAST SEVERAL MONTHS HAVE MADE ME SOMEWHAT LESS THAN A TRUE FAN OF THE SYS. THE DISTR FACTOR MAY HAVE PLAYED A ROLL IN THIS INCIDENT, BUT IF YOU THROW OUT ALL THE SHOULDA'S AND COULDA'S, THE BOTTOM LINE IS THAT THE TCAS SAVED MY BACON ON THIS ONE. I'LL REASSESS MY THINKING ON TCAS.

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.