Narrative:

Cpr X (SW3) was VFR eastbound 25 southwest eri at 11500. Air carrier Y (F100) climb out from eri on 220 degrees heading to 14000. Traffic was exchanged at 15 NM to Y and 12 NM to X. Y advised he had traffic on TCASII. Traffic exchanged again at 5 NM. Y (showing 11300 on mode C) advised he was receiving a TCASII RA and would level below traffic. I issued traffic again to X at 12 O'clock 3 NM 11400 and I believe he's descending. Next radar update showed Y at 11600 and I told X he showed 11600 and climbing. X responded he was now past him. Next radar update showed Y at 11100, and clear of X. Subsequent phone conversation with X (a well-seasoned corporate captain) confirmed that Y was just ahead and to left of SW3 and above his altitude, when Y's nose dropped and descended back through his altitude and crossed his nose at approximately 1 mi and approximately 400 ft below. I believe the TCASII RA caused this event to happen. An uninterrupted climb in my opinion would have presented no confliction. The TCASII RA instructed the F100 to descend, however, before climb energy could be arrested and descent started, the aircraft was already above the conflicting traffic. The descent required by the TCASII alert placed the aircraft in harms way. I believe most of the new technical automation to be a splendid aid to aviation, however, the human logic must be permitted to override obvious shortcomings. TCASII has a history of problems with the software logic. We should reconsider the requirement for capts to react to instructions that are questionable, until the TCASII is much more reliable.

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Original NASA ASRS Text

Title: TCASII LOGIC CAUSED CONFLICT BTWN ACR Y AND CPR X. EVASIVE ACTION TAKEN. SEE AND AVOID CONCEPT.

Narrative: CPR X (SW3) WAS VFR EBOUND 25 SW ERI AT 11500. ACR Y (F100) CLBOUT FROM ERI ON 220 DEGS HDG TO 14000. TFC WAS EXCHANGED AT 15 NM TO Y AND 12 NM TO X. Y ADVISED HE HAD TFC ON TCASII. TFC EXCHANGED AGAIN AT 5 NM. Y (SHOWING 11300 ON MODE C) ADVISED HE WAS RECEIVING A TCASII RA AND WOULD LEVEL BELOW TFC. I ISSUED TFC AGAIN TO X AT 12 O'CLOCK 3 NM 11400 AND I BELIEVE HE'S DSNDING. NEXT RADAR UPDATE SHOWED Y AT 11600 AND I TOLD X HE SHOWED 11600 AND CLBING. X RESPONDED HE WAS NOW PAST HIM. NEXT RADAR UPDATE SHOWED Y AT 11100, AND CLR OF X. SUBSEQUENT PHONE CONVERSATION WITH X (A WELL-SEASONED CORPORATE CAPT) CONFIRMED THAT Y WAS JUST AHEAD AND TO L OF SW3 AND ABOVE HIS ALT, WHEN Y'S NOSE DROPPED AND DSNDED BACK THROUGH HIS ALT AND CROSSED HIS NOSE AT APPROX 1 MI AND APPROX 400 FT BELOW. I BELIEVE THE TCASII RA CAUSED THIS EVENT TO HAPPEN. AN UNINTERRUPTED CLIMB IN MY OPINION WOULD HAVE PRESENTED NO CONFLICTION. THE TCASII RA INSTRUCTED THE F100 TO DSND, HOWEVER, BEFORE CLB ENERGY COULD BE ARRESTED AND DSCNT STARTED, THE ACFT WAS ALREADY ABOVE THE CONFLICTING TFC. THE DSCNT REQUIRED BY THE TCASII ALERT PLACED THE ACFT IN HARMS WAY. I BELIEVE MOST OF THE NEW TECHNICAL AUTOMATION TO BE A SPLENDID AID TO AVIATION, HOWEVER, THE HUMAN LOGIC MUST BE PERMITTED TO OVERRIDE OBVIOUS SHORTCOMINGS. TCASII HAS A HISTORY OF PROBS WITH THE SOFTWARE LOGIC. WE SHOULD RECONSIDER THE REQUIREMENT FOR CAPTS TO REACT TO INSTRUCTIONS THAT ARE QUESTIONABLE, UNTIL THE TCASII IS MUCH MORE RELIABLE.

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.