Narrative:

This narrative deals with a TCASII RA received while on approach. On a left base leg at 5000 ft, under radar vectors, we received a TCASII TA which rapidly became a TCASII RA. The conflicting traffic appeared to be ahead and level at our altitude. The RA commanded 'descend, descend!' we began a descent and were at 4900 ft when ATC gave us a TA, a right turn to 350 degrees, then an immediate right turn to 350 degrees and climb to 6000 ft. We adhered to ATC's instructions even though the TCASII was telling us to descend. This was a very stressful maneuver for the crew. The TCASII then instructed us to 'climb' then shortly followed by another 'descend,' then 'monitor vertical speed,' to 'clear of conflict.' the entire event took approximately 30-45 seconds. We elected to climb given the controller's instruction and given our current altitude, were uncertain of terrain clearance had TCASII continued the descent command. Callback conversation with reporter revealed the following: the reporting captain is sure that this was not a false alarm. Sometime during this incident, the approach controller said something like 'one got away from us on the other side.' cvg was landing on parallel runways 18 and an aircraft that was to land on runway 18R failed to turn when requested, putting 2 aircraft head-to-head. The reporter believes that his TCASII was working properly. The reporter finds that TCASII can be a nuisance at times. The reporter's air carrier flight manual suggests that the flcs can ignore TCASII when it is apparent that ATC has a good handle on the traffic situation as in this case.

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Original NASA ASRS Text

Title: AN ACR MLG IGNORED HIS TCASII INSTRUCTIONS AS HE WAS BEING GIVEN URGENT AND CONTRADICTORY INSTRUCTIONS BY TRACON.

Narrative: THIS NARRATIVE DEALS WITH A TCASII RA RECEIVED WHILE ON APCH. ON A L BASE LEG AT 5000 FT, UNDER RADAR VECTORS, WE RECEIVED A TCASII TA WHICH RAPIDLY BECAME A TCASII RA. THE CONFLICTING TFC APPEARED TO BE AHEAD AND LEVEL AT OUR ALT. THE RA COMMANDED 'DSND, DSND!' WE BEGAN A DSCNT AND WERE AT 4900 FT WHEN ATC GAVE US A TA, A R TURN TO 350 DEGS, THEN AN IMMEDIATE R TURN TO 350 DEGS AND CLB TO 6000 FT. WE ADHERED TO ATC'S INSTRUCTIONS EVEN THOUGH THE TCASII WAS TELLING US TO DSND. THIS WAS A VERY STRESSFUL MANEUVER FOR THE CREW. THE TCASII THEN INSTRUCTED US TO 'CLB' THEN SHORTLY FOLLOWED BY ANOTHER 'DSND,' THEN 'MONITOR VERT SPD,' TO 'CLR OF CONFLICT.' THE ENTIRE EVENT TOOK APPROX 30-45 SECONDS. WE ELECTED TO CLB GIVEN THE CTLR'S INSTRUCTION AND GIVEN OUR CURRENT ALT, WERE UNCERTAIN OF TERRAIN CLRNC HAD TCASII CONTINUED THE DSCNT COMMAND. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING: THE RPTING CAPT IS SURE THAT THIS WAS NOT A FALSE ALARM. SOMETIME DURING THIS INCIDENT, THE APCH CTLR SAID SOMETHING LIKE 'ONE GOT AWAY FROM US ON THE OTHER SIDE.' CVG WAS LNDG ON PARALLEL RWYS 18 AND AN ACFT THAT WAS TO LAND ON RWY 18R FAILED TO TURN WHEN REQUESTED, PUTTING 2 ACFT HEAD-TO-HEAD. THE RPTR BELIEVES THAT HIS TCASII WAS WORKING PROPERLY. THE RPTR FINDS THAT TCASII CAN BE A NUISANCE AT TIMES. THE RPTR'S ACR FLT MANUAL SUGGESTS THAT THE FLCS CAN IGNORE TCASII WHEN IT IS APPARENT THAT ATC HAS A GOOD HANDLE ON THE TFC SIT AS IN THIS CASE.

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.