Narrative:

Flight departed las on runway 01 flying the SID. We climbed on runway heading to the las 2 DME and turned to 070 degrees to intercept the lax 039 degree right on las tower frequency. Las departure was working a light aircraft traveling n-s just east of the airport. That aircraft had been advised of our departure and had reported us in sight before we joined the las departure frequency. As we climbed through 5000' MSL (2000' AGL) on the 070 degree heading, we received a TA showing traffic 12 O'clock, 300' high, level. Almost immediately we received an RA showing traffic at 12 O'clock, 200' high, level. At this time our vsi rate was approximately 2000 FPM. The only visibility traffic we could identify was the right distance and altitude, but was at our 2 O'clock position. As we were unsure that was the correct traffic and we had terrain clearance straight ahead, I adhered to the RA. The initial RA command was, 'descend.' due to the time it took to transition from a 2000 FPM climb to the required descent, we received an additional RA to, 'increase descent.' at approximately 4500' MSL (1500' AGL), the TCAS was still commanding a 2500 FPM descent into rising terrain. Shortly thereafter, we received a 'monitor vertical speed' command with the TCAS display allowing for no climb. We leveled at 4200' MSL (1200' AGL) for about 20 seconds before receiving a 'clear of conflict.' during this resolution, we deviated from the assigned SID by not intercepting the 039 degree right as this would have turned us into the 5200' peak that underlies the departure. I have several concerns as a result of this experience. First, I question the TCAS decision to resolve with a descent. With traffic 2 mi away and only 200' above us, it would have been must safer to resolve with a climb. Far's, however, prevent us from acting opp to an RA. Second, I question whether the TCAS should be on RA at all during departures through mountainous terrain. At night on ir low visibility, I would have been unable to maneuver between the traffic and the 5200' peak immediately to our left. Had we either made our turnout to 070 degrees more gradually, or had followed the SID to intercept the las 039 degree right, this resolution would have ended with us impacting the peak. In flat terrain, the GPWS would have provided some protection against rising terrain, but not in this environment. Third, ATC must be made aware that even if conflicting traffic has reported us in sight and agreed to remain clear, they still remain a threat to the TCAS. If they allow any unknown traffic inside our conflict area, we will have to response to the RA, creating at least clearance deviations and possibly a disaster.

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Original NASA ASRS Text

Title: FLT CREW OF LGT HAD TCAS TA AND THEN RA TO DESCEND TO AVOID KNOWN TRAFFIC REPORTED BY TRACON. COMPLYING WITH PRESCRIBED TCASII PROCS CAUSED THE FLT TO DESCEND TOWARD TERRAIN.

Narrative: FLT DEPARTED LAS ON RWY 01 FLYING THE SID. WE CLBED ON RWY HDG TO THE LAS 2 DME AND TURNED TO 070 DEGS TO INTERCEPT THE LAX 039 DEG R ON LAS TWR FREQ. LAS DEP WAS WORKING A LIGHT ACFT TRAVELING N-S JUST E OF THE ARPT. THAT ACFT HAD BEEN ADVISED OF OUR DEP AND HAD RPTED US IN SIGHT BEFORE WE JOINED THE LAS DEP FREQ. AS WE CLBED THROUGH 5000' MSL (2000' AGL) ON THE 070 DEG HDG, WE RECEIVED A TA SHOWING TFC 12 O'CLOCK, 300' HIGH, LEVEL. ALMOST IMMEDIATELY WE RECEIVED AN RA SHOWING TFC AT 12 O'CLOCK, 200' HIGH, LEVEL. AT THIS TIME OUR VSI RATE WAS APPROX 2000 FPM. THE ONLY VIS TFC WE COULD IDENT WAS THE RIGHT DISTANCE AND ALT, BUT WAS AT OUR 2 O'CLOCK POS. AS WE WERE UNSURE THAT WAS THE CORRECT TFC AND WE HAD TERRAIN CLRNC STRAIGHT AHEAD, I ADHERED TO THE RA. THE INITIAL RA COMMAND WAS, 'DSND.' DUE TO THE TIME IT TOOK TO TRANSITION FROM A 2000 FPM CLB TO THE REQUIRED DSNT, WE RECEIVED AN ADDITIONAL RA TO, 'INCREASE DSNT.' AT APPROX 4500' MSL (1500' AGL), THE TCAS WAS STILL COMMANDING A 2500 FPM DSNT INTO RISING TERRAIN. SHORTLY THEREAFTER, WE RECEIVED A 'MONITOR VERT SPD' COMMAND WITH THE TCAS DISPLAY ALLOWING FOR NO CLB. WE LEVELED AT 4200' MSL (1200' AGL) FOR ABOUT 20 SECS BEFORE RECEIVING A 'CLR OF CONFLICT.' DURING THIS RESOLUTION, WE DEVIATED FROM THE ASSIGNED SID BY NOT INTERCEPTING THE 039 DEG R AS THIS WOULD HAVE TURNED US INTO THE 5200' PEAK THAT UNDERLIES THE DEP. I HAVE SEVERAL CONCERNS AS A RESULT OF THIS EXPERIENCE. FIRST, I QUESTION THE TCAS DECISION TO RESOLVE WITH A DSNT. WITH TFC 2 MI AWAY AND ONLY 200' ABOVE US, IT WOULD HAVE BEEN MUST SAFER TO RESOLVE WITH A CLB. FAR'S, HOWEVER, PREVENT US FROM ACTING OPP TO AN RA. SECOND, I QUESTION WHETHER THE TCAS SHOULD BE ON RA AT ALL DURING DEPS THROUGH MOUNTAINOUS TERRAIN. AT NIGHT ON IR LOW VISIBILITY, I WOULD HAVE BEEN UNABLE TO MANEUVER BTWN THE TFC AND THE 5200' PEAK IMMEDIATELY TO OUR LEFT. HAD WE EITHER MADE OUR TURNOUT TO 070 DEGS MORE GRADUALLY, OR HAD FOLLOWED THE SID TO INTERCEPT THE LAS 039 DEG R, THIS RESOLUTION WOULD HAVE ENDED WITH US IMPACTING THE PEAK. IN FLAT TERRAIN, THE GPWS WOULD HAVE PROVIDED SOME PROTECTION AGAINST RISING TERRAIN, BUT NOT IN THIS ENVIRONMENT. THIRD, ATC MUST BE MADE AWARE THAT EVEN IF CONFLICTING TFC HAS RPTED US IN SIGHT AND AGREED TO REMAIN CLR, THEY STILL REMAIN A THREAT TO THE TCAS. IF THEY ALLOW ANY UNKNOWN TFC INSIDE OUR CONFLICT AREA, WE WILL HAVE TO RESPONSE TO THE RA, CREATING AT LEAST CLRNC DEVIATIONS AND POSSIBLY A DISASTER.

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.