Narrative:

Air carrier X departed and reported on the departure control frequency. I instructed the pilot to climb and maintain 11000 ft and pilot acknowledged. After a pause I issued a right turn to 190 degrees and pilot informed me that he had traffic and I asked him to repeat himself and he said 'we are avoiding traffic' and I acknowledged. After a brief pause I observed the aircraft descending and asked him what his intentions were and he stated that he was turning to 190 degrees and climbing to 11000 ft. I then asked the pilot if he had responded to TCASII and had an RA and stated to the affirmative. I asked him what the RA instructed him to do and why. He answered 'maximum descent traffic above me at 0 altitude.' I advised that there was no traffic above him or any within 6 mi and my concern of a maximum descent at such an altitude above the ground. He then stated he was unsure of the reason but it was on the fdr and he would have maintenance check into it. In this example, TCASII instructed an aircraft to descend rapidly from 2800 ft, in mountainous terrain, with no regard to terrain or obstruction elevation and no traffic in proximity. In this case, I believe that had the WX been IFR, pilot unfamiliar with landscape, and pilot complied blindly to this RA, ground proximity would have been a factor. There was no traffic in the immediate vicinity, much less above him. This was an awakening to see a sightless computer jeopardize an aircraft, its crew and passenger, by telling them to execute a rapid descent, into god knows what, from already a low altitude, with no consideration of terrain or obstruction elevation.

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Original NASA ASRS Text

Title: ACR X FALSE WARNING ON TCASII RA CAUSED CFTT. PLTDEV.

Narrative: ACR X DEPARTED AND RPTED ON THE DEP CTL FREQ. I INSTRUCTED THE PLT TO CLB AND MAINTAIN 11000 FT AND PLT ACKNOWLEDGED. AFTER A PAUSE I ISSUED A R TURN TO 190 DEGS AND PLT INFORMED ME THAT HE HAD TFC AND I ASKED HIM TO REPEAT HIMSELF AND HE SAID 'WE ARE AVOIDING TFC' AND I ACKNOWLEDGED. AFTER A BRIEF PAUSE I OBSERVED THE ACFT DSNDING AND ASKED HIM WHAT HIS INTENTIONS WERE AND HE STATED THAT HE WAS TURNING TO 190 DEGS AND CLBING TO 11000 FT. I THEN ASKED THE PLT IF HE HAD RESPONDED TO TCASII AND HAD AN RA AND STATED TO THE AFFIRMATIVE. I ASKED HIM WHAT THE RA INSTRUCTED HIM TO DO AND WHY. HE ANSWERED 'MAX DSCNT TFC ABOVE ME AT 0 ALT.' I ADVISED THAT THERE WAS NO TFC ABOVE HIM OR ANY WITHIN 6 MI AND MY CONCERN OF A MAX DSCNT AT SUCH AN ALT ABOVE THE GND. HE THEN STATED HE WAS UNSURE OF THE REASON BUT IT WAS ON THE FDR AND HE WOULD HAVE MAINT CHK INTO IT. IN THIS EXAMPLE, TCASII INSTRUCTED AN ACFT TO DSND RAPIDLY FROM 2800 FT, IN MOUNTAINOUS TERRAIN, WITH NO REGARD TO TERRAIN OR OBSTRUCTION ELEVATION AND NO TFC IN PROX. IN THIS CASE, I BELIEVE THAT HAD THE WX BEEN IFR, PLT UNFAMILIAR WITH LANDSCAPE, AND PLT COMPLIED BLINDLY TO THIS RA, GND PROX WOULD HAVE BEEN A FACTOR. THERE WAS NO TFC IN THE IMMEDIATE VICINITY, MUCH LESS ABOVE HIM. THIS WAS AN AWAKENING TO SEE A SIGHTLESS COMPUTER JEOPARDIZE AN ACFT, ITS CREW AND PAX, BY TELLING THEM TO EXECUTE A RAPID DSCNT, INTO GOD KNOWS WHAT, FROM ALREADY A LOW ALT, WITH NO CONSIDERATION OF TERRAIN OR OBSTRUCTION ELEVATION.

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.