Narrative:

Air carrier a reported on the frequency and was issued the runway to expect. After a brief pause, the pilot advised me that he would have to avoid traffic off his nose and 500 ft below. I acknowledged the traffic, asked if was receiving a RA and asked his intentions. He stated that TCASII was instructing him to climb and that he would do so until visually contacting the traffic. I informed the pilot to take whatever action would be necessary to avoid the traffic and informed adjacent sectors that may become affected by any maneuver the aircraft could take. I observed air carrier a climbing and asked if that would be all that was required to comply with the RA and was acknowledged to the affirmative. Now the whole time prior to, during and succeeding this, appearance to TCASII, conflicting traffic never changed course or left an altitude of 9500 ft. As most of us know, 500 ft is approved vertical separation, in class 'C' airspace, between and IFR and VFR aircraft. These 2 aircraft were never a conflict. Projected courses would have caused them to pass each other with more than standard lateral separation, yet TCASII says they will hit therefore instructing the equipped pilot to avoid by a means that has the potential to impact other aircraft and/or violate other controller's airspace and dramatically increase workload. In the last week I've seen and reported 2 occurrences of TCASII events and its ideas of how to miss either nonexistent traffic or traffic that was already separated by vertical and/or lateral means within prescribed minima. Now this TCASII, as it is intended, might and should be a good thing, but under the current technology and programming it lacks the ability to incorporate terrain/obstruction elevation in its determining traffic avoidance as well as not knowing what is adequate separation between other aircraft. Considering this, it is all too possible for TCASII to instruct an air crew to avoid traffic and causing the aircraft to climb into another or descend into a radio tower, mountain, skyscraper or another aircraft. Meanwhile, once the controller hears the words 'RA' from one of our aircraft, in our jurisdiction, we are supposed to bite our tongues, situation on our hands and watch without offering any advice or suggestions, while TCASII takes over the skies for that brief moment, by telling air crews how to avoid unseen traffic without any regard for other traffic or terrain/obstruction elevation. When I have asked air crews why a particular or preceding event has occurred the response has been one of confusion and with reservation, but always having their maintenance technicians look into it.

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Original NASA ASRS Text

Title: PLTDEV -- ACR A DEVIATED FROM ASSIGNED ALT DUE TO TCASII ALERT. CTLR WAS INFORMED OF EVASIVE MANEUVER TO BE TAKEN.

Narrative: ACR A RPTED ON THE FREQ AND WAS ISSUED THE RWY TO EXPECT. AFTER A BRIEF PAUSE, THE PLT ADVISED ME THAT HE WOULD HAVE TO AVOID TFC OFF HIS NOSE AND 500 FT BELOW. I ACKNOWLEDGED THE TFC, ASKED IF WAS RECEIVING A RA AND ASKED HIS INTENTIONS. HE STATED THAT TCASII WAS INSTRUCTING HIM TO CLB AND THAT HE WOULD DO SO UNTIL VISUALLY CONTACTING THE TFC. I INFORMED THE PLT TO TAKE WHATEVER ACTION WOULD BE NECESSARY TO AVOID THE TFC AND INFORMED ADJACENT SECTORS THAT MAY BECOME AFFECTED BY ANY MANEUVER THE ACFT COULD TAKE. I OBSERVED ACR A CLBING AND ASKED IF THAT WOULD BE ALL THAT WAS REQUIRED TO COMPLY WITH THE RA AND WAS ACKNOWLEDGED TO THE AFFIRMATIVE. NOW THE WHOLE TIME PRIOR TO, DURING AND SUCCEEDING THIS, APPEARANCE TO TCASII, CONFLICTING TFC NEVER CHANGED COURSE OR LEFT AN ALT OF 9500 FT. AS MOST OF US KNOW, 500 FT IS APPROVED VERT SEPARATION, IN CLASS 'C' AIRSPACE, BTWN AND IFR AND VFR ACFT. THESE 2 ACFT WERE NEVER A CONFLICT. PROJECTED COURSES WOULD HAVE CAUSED THEM TO PASS EACH OTHER WITH MORE THAN STANDARD LATERAL SEPARATION, YET TCASII SAYS THEY WILL HIT THEREFORE INSTRUCTING THE EQUIPPED PLT TO AVOID BY A MEANS THAT HAS THE POTENTIAL TO IMPACT OTHER ACFT AND/OR VIOLATE OTHER CTLR'S AIRSPACE AND DRAMATICALLY INCREASE WORKLOAD. IN THE LAST WK I'VE SEEN AND RPTED 2 OCCURRENCES OF TCASII EVENTS AND ITS IDEAS OF HOW TO MISS EITHER NONEXISTENT TFC OR TFC THAT WAS ALREADY SEPARATED BY VERT AND/OR LATERAL MEANS WITHIN PRESCRIBED MINIMA. NOW THIS TCASII, AS IT IS INTENDED, MIGHT AND SHOULD BE A GOOD THING, BUT UNDER THE CURRENT TECHNOLOGY AND PROGRAMMING IT LACKS THE ABILITY TO INCORPORATE TERRAIN/OBSTRUCTION ELEVATION IN ITS DETERMINING TFC AVOIDANCE AS WELL AS NOT KNOWING WHAT IS ADEQUATE SEPARATION BTWN OTHER ACFT. CONSIDERING THIS, IT IS ALL TOO POSSIBLE FOR TCASII TO INSTRUCT AN AIR CREW TO AVOID TFC AND CAUSING THE ACFT TO CLB INTO ANOTHER OR DSND INTO A RADIO TWR, MOUNTAIN, SKYSCRAPER OR ANOTHER ACFT. MEANWHILE, ONCE THE CTLR HEARS THE WORDS 'RA' FROM ONE OF OUR ACFT, IN OUR JURISDICTION, WE ARE SUPPOSED TO BITE OUR TONGUES, SIT ON OUR HANDS AND WATCH WITHOUT OFFERING ANY ADVICE OR SUGGESTIONS, WHILE TCASII TAKES OVER THE SKIES FOR THAT BRIEF MOMENT, BY TELLING AIR CREWS HOW TO AVOID UNSEEN TFC WITHOUT ANY REGARD FOR OTHER TFC OR TERRAIN/OBSTRUCTION ELEVATION. WHEN I HAVE ASKED AIR CREWS WHY A PARTICULAR OR PRECEDING EVENT HAS OCCURRED THE RESPONSE HAS BEEN ONE OF CONFUSION AND WITH RESERVATION, BUT ALWAYS HAVING THEIR MAINT TECHNICIANS LOOK INTO IT.

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.