An air carrier widebody transport crew descended in response to a TCASII command.

Attributes
ACN	256322
Time
Date	199311
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : sny
State Reference	NE
Altitude	msl bound lower : 35000 msl bound upper : 37000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : den
Operator	common carrier : air carrier
Make Model Name	Widebody, Low Wing, 3 Turbojet Eng
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 200 flight time total : 6000 flight time type : 500
ASRS Report	256322
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time total : 17000 flight time type : 4500
ASRS Report	256454
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : published procedure non adherence : clearance non adherence : far other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : took evasive action
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

I noticed the TCASII was placarded inoperative. I tested the TCASII as per SOP and it tested 'passed.' upon takeoff I set the TCASII to RA/TA, based on the 'passed' test. The vvi then stated TA only. Based on the passed test and TA only, I left the unit on RA/TA. Unknown to me, it is a maintenance function to pull and collar the circuit breaker, yet this was never accomplished. Sometime during cruise, the TA only light on the vvi must have extinguished, I'm guessing, as we were given a 'descend, descend now' twice, followed by 'increased descent.' there was a yellow DOT right on our position with a '-00' altitude. We pushed nose over in approximately 1.5 seconds and lost 1200 ft. We never did get a 'clear of traffic' advisory. We called ZDV and asked if they showed any traffic near us, and they stated no. We then leveled off at 35800 ft and started back to 37000 ft. We called level 37000 ft when so. System tested 'passed' immediately after the erroneous advisory.

Original NASA ASRS Text

Title: AN ACR WDB CREW DSNDED IN RESPONSE TO A TCASII COMMAND.

Narrative: I NOTICED THE TCASII WAS PLACARDED INOP. I TESTED THE TCASII AS PER SOP AND IT TESTED 'PASSED.' UPON TKOF I SET THE TCASII TO RA/TA, BASED ON THE 'PASSED' TEST. THE VVI THEN STATED TA ONLY. BASED ON THE PASSED TEST AND TA ONLY, I LEFT THE UNIT ON RA/TA. UNKNOWN TO ME, IT IS A MAINT FUNCTION TO PULL AND COLLAR THE CIRCUIT BREAKER, YET THIS WAS NEVER ACCOMPLISHED. SOMETIME DURING CRUISE, THE TA ONLY LIGHT ON THE VVI MUST HAVE EXTINGUISHED, I'M GUESSING, AS WE WERE GIVEN A 'DSND, DSND NOW' TWICE, FOLLOWED BY 'INCREASED DSCNT.' THERE WAS A YELLOW DOT RIGHT ON OUR POS WITH A '-00' ALT. WE PUSHED NOSE OVER IN APPROX 1.5 SECONDS AND LOST 1200 FT. WE NEVER DID GET A 'CLR OF TFC' ADVISORY. WE CALLED ZDV AND ASKED IF THEY SHOWED ANY TFC NEAR US, AND THEY STATED NO. WE THEN LEVELED OFF AT 35800 FT AND STARTED BACK TO 37000 FT. WE CALLED LEVEL 37000 FT WHEN SO. SYS TESTED 'PASSED' IMMEDIATELY AFTER THE ERRONEOUS ADVISORY.

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.