A DC10 flight crew report on a false alarm being triggered into their TCASII system by a malfunctioning mode C transponder from opposite direction traffic 2000 ft above them near bff, northeast.

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Attributes
ACN	455616
Time
Date	199911
Day	Wed
Local Time Of Day	0601 To 1200
Place
State Reference	NE
Altitude	msl bound lower : 34000 msl bound upper : 35000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdv.artcc
Operator	common carrier : air carrier
Make Model Name	DC-10 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	cruise : level
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zdv.artcc
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : commercial pilot : atp
Experience	flight time last 90 days : 220 flight time total : 14000 flight time type : 3000
ASRS Report	455616
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : flight engineer pilot : instrument pilot : commercial
Experience	flight time last 90 days : 200 flight time total : 3500 flight time type : 550
ASRS Report	455620
Events
Anomaly	aircraft equipment problem : less severe
Independent Detector	atc equipment other atc equipment : mode c aircraft equipment : tcas other controllera other flight crewa other flight crewb
Resolutory Action	aircraft : equipment problem dissipated flight crew : took evasive action flight crew : returned to assigned altitude
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

In cruise at FL350, TCASII sounded 'traffic, traffic.' I looked at display reaching to reduce range from 40 NM to 5 NM. Before my finger touched the button, the TCASII RA sounded 'descend, descend.' I turned off the autoplt, pushed the nose down, and advised the copilot to advise ATC of TCASII descent. ZDV asked 'who called?' and we responded with our flight number and advised we were at FL340 climbing back to FL350 due to TCASII descent RA. ZDV said his scope showed conflict traffic at FL350 which then switched to FL370 as he watched. We returned to FL350 and flight continued uneventfully. Apparently an electronic glitch. (We did see an opposite direction aircraft well above our altitude at the time of the RA.) supplemental information from acn 455620: the controller asked if anything was wrong and we advised him of the RA. He responded that the only other traffic was at FL370 and then advised he just got a radar swap from FL370/FL350/FL370. The only traffic we could identify visually was the traffic at FL370 which was passing us and probably caused the glitch.

Original NASA ASRS Text

Title: A DC10 FLC RPT ON A FALSE ALARM BEING TRIGGERED INTO THEIR TCASII SYS BY A MALFUNCTIONING MODE C XPONDER FROM OPPOSITE DIRECTION TFC 2000 FT ABOVE THEM NEAR BFF, NE.

Narrative: IN CRUISE AT FL350, TCASII SOUNDED 'TFC, TFC.' I LOOKED AT DISPLAY REACHING TO REDUCE RANGE FROM 40 NM TO 5 NM. BEFORE MY FINGER TOUCHED THE BUTTON, THE TCASII RA SOUNDED 'DSND, DSND.' I TURNED OFF THE AUTOPLT, PUSHED THE NOSE DOWN, AND ADVISED THE COPLT TO ADVISE ATC OF TCASII DSCNT. ZDV ASKED 'WHO CALLED?' AND WE RESPONDED WITH OUR FLT NUMBER AND ADVISED WE WERE AT FL340 CLBING BACK TO FL350 DUE TO TCASII DSCNT RA. ZDV SAID HIS SCOPE SHOWED CONFLICT TFC AT FL350 WHICH THEN SWITCHED TO FL370 AS HE WATCHED. WE RETURNED TO FL350 AND FLT CONTINUED UNEVENTFULLY. APPARENTLY AN ELECTRONIC GLITCH. (WE DID SEE AN OPPOSITE DIRECTION ACFT WELL ABOVE OUR ALT AT THE TIME OF THE RA.) SUPPLEMENTAL INFO FROM ACN 455620: THE CTLR ASKED IF ANYTHING WAS WRONG AND WE ADVISED HIM OF THE RA. HE RESPONDED THAT THE ONLY OTHER TFC WAS AT FL370 AND THEN ADVISED HE JUST GOT A RADAR SWAP FROM FL370/FL350/FL370. THE ONLY TFC WE COULD IDENT VISUALLY WAS THE TFC AT FL370 WHICH WAS PASSING US AND PROBABLY CAUSED THE GLITCH.

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.