TCASII. Faulty transponder, mode C from other aircraft caused erroneous RA.

Attributes
ACN	316817
Time
Date	199509
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : gjt
State Reference	CO
Altitude	msl bound lower : 30300 msl bound upper : 31000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zdv
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other
Route In Use	enroute 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 : 150 flight time total : 15900 flight time type : 1500
ASRS Report	316817
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 150 flight time total : 7500 flight time type : 2000
ASRS Report	316705
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 : returned to intended course or assigned course flight crew : took evasive action
Consequence	faa : reviewed incident with flight crew
Supplementary
Air Traffic Incident	other

Narrative:

In cruise FL310, we received TCASII RA 'traffic' followed by 'descend' 'descend now' command. We left FL310, descended to FL303 then received 'clear of conflict' and returned to FL310. We advised ATC. He then advised of traffic at FL290 with possible mode C transponder problem. Our TCASII had shown targets at FL290 and FL312 super-imposed at 12 O'clock close range. We did not see traffic visually.

Original NASA ASRS Text

Title: TCASII. FAULTY XPONDER, MODE C FROM OTHER ACFT CAUSED ERRONEOUS RA.

Narrative: IN CRUISE FL310, WE RECEIVED TCASII RA 'TFC' FOLLOWED BY 'DSND' 'DSND NOW' COMMAND. WE LEFT FL310, DSNDED TO FL303 THEN RECEIVED 'CLR OF CONFLICT' AND RETURNED TO FL310. WE ADVISED ATC. HE THEN ADVISED OF TFC AT FL290 WITH POSSIBLE MODE C XPONDER PROB. OUR TCASII HAD SHOWN TARGETS AT FL290 AND FL312 SUPER-IMPOSED AT 12 O'CLOCK CLOSE RANGE. WE DID NOT SEE TFC VISUALLY.

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.