Flight crew takes evasive action prompted by TCASII false RA.

Attributes
ACN	300241
Time
Date	199503
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : dxo airport : dtw
State Reference	MI
Altitude	msl bound lower : 5500 msl bound upper : 6000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : dtw
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
Flight Plan	IFR
Aircraft 2
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	other : unknown
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 210 flight time total : 5000 flight time type : 210
ASRS Report	300241
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
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 : took evasive action
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Level at 6000 ft MSL, we received a TCASII advisory. TCASII display showed a target at about 1 NM, 9 O'clock position, at our altitude (00 ft). It almost immediately turned into a TCASII RA and TCASII announced 'descend, descend.' captain disconnected autoplt and followed the TCASII instructions, descended about 400-500 ft (5500 ft MSL) when RA stopped without a 'clear of conflict' message. Target now was at 1 NM, 6 O'clock position, 2600 ft below our altitude. We informed detroit approach of our situation and climbed back up to 6000 ft. ATC said there was no conflicting traffic and the traffic below us was level over 2000 ft below us and no factor. Evidently, it was a false RA for reasons unknown.

Original NASA ASRS Text

Title: FLC TAKES EVASIVE ACTION PROMPTED BY TCASII FALSE RA.

Narrative: LEVEL AT 6000 FT MSL, WE RECEIVED A TCASII ADVISORY. TCASII DISPLAY SHOWED A TARGET AT ABOUT 1 NM, 9 O'CLOCK POS, AT OUR ALT (00 FT). IT ALMOST IMMEDIATELY TURNED INTO A TCASII RA AND TCASII ANNOUNCED 'DSND, DSND.' CAPT DISCONNECTED AUTOPLT AND FOLLOWED THE TCASII INSTRUCTIONS, DSNDED ABOUT 400-500 FT (5500 FT MSL) WHEN RA STOPPED WITHOUT A 'CLR OF CONFLICT' MESSAGE. TARGET NOW WAS AT 1 NM, 6 O'CLOCK POS, 2600 FT BELOW OUR ALT. WE INFORMED DETROIT APCH OF OUR SIT AND CLBED BACK UP TO 6000 FT. ATC SAID THERE WAS NO CONFLICTING TFC AND THE TFC BELOW US WAS LEVEL OVER 2000 FT BELOW US AND NO FACTOR. EVIDENTLY, IT WAS A FALSE RA FOR REASONS UNKNOWN.

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.