TCAS RA results in overshooting localizer course and altitude deviation. TCASII.

Attributes
ACN	178134
Time
Date	199104
Day	Sun
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : ord
State Reference	IL
Altitude	msl bound lower : 4500 msl bound upper : 4500
Environment
Flight Conditions	Marginal
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ord
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	descent : approach
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : flight engineer pilot : commercial pilot : atp pilot : private
Experience	flight time last 90 days : 200 flight time total : 6000
ASRS Report	178134
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	controller : issued new clearance other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

At 4500' descending we responded to a TCAS RA to climb. This caused an overshooting of 14L localizer. We were told to ignore TCAS by ATC and vectored back to 14L localizer at ord. Landed 14L uneventfully. My opinion is that the current TCAS system in use is flawed. Too many ambiguous targets. I cannot rely on or trust TCAS commands, especially when ATC tells me to ignore it. I will not use TCAS until it is improved.

Original NASA ASRS Text

Title: TCAS RA RESULTS IN OVERSHOOTING LOCALIZER COURSE AND ALT DEVIATION. TCASII.

Narrative: AT 4500' DSNDING WE RESPONDED TO A TCAS RA TO CLB. THIS CAUSED AN OVERSHOOTING OF 14L LOC. WE WERE TOLD TO IGNORE TCAS BY ATC AND VECTORED BACK TO 14L LOC AT ORD. LANDED 14L UNEVENTFULLY. MY OPINION IS THAT THE CURRENT TCAS SYS IN USE IS FLAWED. TOO MANY AMBIGUOUS TARGETS. I CANNOT RELY ON OR TRUST TCAS COMMANDS, ESPECIALLY WHEN ATC TELLS ME TO IGNORE IT. I WILL NOT USE TCAS UNTIL IT IS IMPROVED.

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.