Air carrier PIC deviates from ATC altitude clearance on signals received from TCASII.

Attributes
ACN	177004
Time
Date	199104
Day	Sun
Local Time Of Day	1201 To 1800
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 other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 185 flight time total : 16200 flight time type : 185
ASRS Report	177004
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : undershoot conflict : airborne less severe non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	controller : issued new clearance other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

On approach to ord, we were being vectored (230 degree heading) for a 14L localizer approach. Descending through 4500', we received a TCAS RA which called for, 'reduce descent,' with the green arc just above and below level flight. I leveled off and in just a couple of seconds got a 'clear of conflict' message. Just a few seconds later we got a TA followed by another RA calling for a climb. As I advanced the throttles, approach control called, giving us a vector back toward the localizer (120 degree heading). The first officer responded that we were getting a TCAS RA and the approach controller told us to ignore the TCAS. We entered the turn per his instructions and continued in to land. If the approach controller had tried calling us earlier, his transmission was covered by the loud TCAS warning. It put us in quite a dilemma with TCAS telling us to do 1 thing and the controller telling us to do another. All 3 TCAS aural messages occurred in less than 1 min.

Original NASA ASRS Text

Title: ACR PIC DEVIATES FROM ATC ALT CLRNC ON SIGNALS RECEIVED FROM TCASII.

Narrative: ON APCH TO ORD, WE WERE BEING VECTORED (230 DEG HDG) FOR A 14L LOC APCH. DSNDING THROUGH 4500', WE RECEIVED A TCAS RA WHICH CALLED FOR, 'REDUCE DSNT,' WITH THE GREEN ARC JUST ABOVE AND BELOW LEVEL FLT. I LEVELED OFF AND IN JUST A COUPLE OF SECS GOT A 'CLR OF CONFLICT' MESSAGE. JUST A FEW SECS LATER WE GOT A TA FOLLOWED BY ANOTHER RA CALLING FOR A CLB. AS I ADVANCED THE THROTTLES, APCH CTL CALLED, GIVING US A VECTOR BACK TOWARD THE LOC (120 DEG HDG). THE F/O RESPONDED THAT WE WERE GETTING A TCAS RA AND THE APCH CTLR TOLD US TO IGNORE THE TCAS. WE ENTERED THE TURN PER HIS INSTRUCTIONS AND CONTINUED IN TO LAND. IF THE APCH CTLR HAD TRIED CALLING US EARLIER, HIS XMISSION WAS COVERED BY THE LOUD TCAS WARNING. IT PUT US IN QUITE A DILEMMA WITH TCAS TELLING US TO DO 1 THING AND THE CTLR TELLING US TO DO ANOTHER. ALL 3 TCAS AURAL MESSAGES OCCURRED IN LESS THAN 1 MIN.

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.