Large transport has false TCASII TA and RA.

Attributes
ACN	284425
Time
Date	199409
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : ord
State Reference	IL
Altitude	msl bound lower : 5000 msl bound upper : 5300
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ord
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent : approach descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : commercial pilot : instrument pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 190 flight time total : 13649 flight time type : 3000
ASRS Report	284425
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : atp pilot : instrument
Events
Anomaly	aircraft equipment problem : critical non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : took evasive action
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

We were descending from 7000-5000 ft MSL on radar vectors. At about 5300 ft MSL in our descent, a red RA target appeared suddenly on the HSI on our nose and the TCASII gave a 'climb' RA followed by 'monitor vertical speed' advisory after we reversed our descent and began a climb per TCASII RA instructions. (We had been continuously in clouds beginning above 7000 ft MSL.) the target suddenly disappeared. No 'clear of conflict' was issued by TCASII, but RA guidance also disappeared. We leveled at about 5700 ft MSL. I advised ATC and asked for and received clearance to 4000 ft MSL to get beneath the cloud bases. Chicago approach control confirmed that they had no conflicting traffic, which was also the case for a previous TA we had received by TCASII while at 7000 ft MSL, where we were also in the clouds. Surface temperature at ord was about 58 degrees fahrenheit. I suspect that the clouds and moisture caused false TA's/RA's, and we wrote up the TCASII after landing. There was apparently no actual traffic conflict.

Original NASA ASRS Text

Title: LGT HAS FALSE TCASII TA AND RA.

Narrative: WE WERE DSNDING FROM 7000-5000 FT MSL ON RADAR VECTORS. AT ABOUT 5300 FT MSL IN OUR DSCNT, A RED RA TARGET APPEARED SUDDENLY ON THE HSI ON OUR NOSE AND THE TCASII GAVE A 'CLB' RA FOLLOWED BY 'MONITOR VERT SPD' ADVISORY AFTER WE REVERSED OUR DSCNT AND BEGAN A CLB PER TCASII RA INSTRUCTIONS. (WE HAD BEEN CONTINUOUSLY IN CLOUDS BEGINNING ABOVE 7000 FT MSL.) THE TARGET SUDDENLY DISAPPEARED. NO 'CLR OF CONFLICT' WAS ISSUED BY TCASII, BUT RA GUIDANCE ALSO DISAPPEARED. WE LEVELED AT ABOUT 5700 FT MSL. I ADVISED ATC AND ASKED FOR AND RECEIVED CLRNC TO 4000 FT MSL TO GET BENEATH THE CLOUD BASES. CHICAGO APCH CTL CONFIRMED THAT THEY HAD NO CONFLICTING TFC, WHICH WAS ALSO THE CASE FOR A PREVIOUS TA WE HAD RECEIVED BY TCASII WHILE AT 7000 FT MSL, WHERE WE WERE ALSO IN THE CLOUDS. SURFACE TEMP AT ORD WAS ABOUT 58 DEGS FAHRENHEIT. I SUSPECT THAT THE CLOUDS AND MOISTURE CAUSED FALSE TA'S/RA'S, AND WE WROTE UP THE TCASII AFTER LNDG. THERE WAS APPARENTLY NO ACTUAL TFC CONFLICT.

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.