B757-200 receives TCAS TA while on approach to den in IMC. When clear of clouds no traffic noted in ...

Attributes
ACN	700991
Time
Date	200606
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : den.airport
State Reference	CO
Altitude	agl single value : 2300
Environment
Flight Conditions	IMC
Aircraft 1
Controlling Facilities	tower : den.tower
Operator	common carrier : air carrier
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer & glide slope : 35l
Flight Phase	descent : approach
Route In Use	approach : instrument precision
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 240 flight time total : 13200 flight time type : 6000
ASRS Report	700991
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	other flight crewa other flight crewb
Resolutory Action	none taken : anomaly accepted
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

During IMC approach; observed TCAS showing an aircraft at approximately 7000 ft MSL in front of aircraft. Aircraft appeared to cross in front of us and then move off to our right. At 6400 ft MSL TCAS showed an aircraft TA at our altitude just ahead of aircraft. At this time we were still IMC. First officer observed that this may have been a TCAS anomaly. Exited the cloud bases at 900 ft AGL. No aircraft observed near our aircraft. Continued approach and landing with no further incident. This TCAS incident should be looked into as it caused a go/no-go decision that could have turned out much differently. Is our TCAS to be trusted? This is my first time seeing an event such as this at low level. When TCAS was new I had seen similar events but at cruise.

Original NASA ASRS Text

Title: B757-200 RECEIVES TCAS TA WHILE ON APCH TO DEN IN IMC. WHEN CLR OF CLOUDS NO TFC NOTED IN THE VICINITY.

Narrative: DURING IMC APCH; OBSERVED TCAS SHOWING AN ACFT AT APPROX 7000 FT MSL IN FRONT OF ACFT. ACFT APPEARED TO CROSS IN FRONT OF US AND THEN MOVE OFF TO OUR R. AT 6400 FT MSL TCAS SHOWED AN ACFT TA AT OUR ALT JUST AHEAD OF ACFT. AT THIS TIME WE WERE STILL IMC. FO OBSERVED THAT THIS MAY HAVE BEEN A TCAS ANOMALY. EXITED THE CLOUD BASES AT 900 FT AGL. NO ACFT OBSERVED NEAR OUR ACFT. CONTINUED APCH AND LNDG WITH NO FURTHER INCIDENT. THIS TCAS INCIDENT SHOULD BE LOOKED INTO AS IT CAUSED A GO/NO-GO DECISION THAT COULD HAVE TURNED OUT MUCH DIFFERENTLY. IS OUR TCAS TO BE TRUSTED? THIS IS MY FIRST TIME SEEING AN EVENT SUCH AS THIS AT LOW LEVEL. WHEN TCAS WAS NEW I HAD SEEN SIMILAR EVENTS BUT AT CRUISE.

Data retrieved from NASA's ASRS site as of January 2009 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.

B757-200 receives TCAS TA while on approach to den in IMC. When clear of clouds no traffic noted in the vicinity.