A B737-300 RECEIVED A GPWS CAUTION APCHING RNO RWY 34R LOW ON A MANUALLY BUILT FMS APCH.

Narrative

ATIS RPTED THAT WINDS AT RNO WERE OUT OF THE N AT 9 KTS AND VISUAL APCHS TO RWY 34R WERE IN USE. THE ILS AND BACK COURSE LOC WERE OTS AND RWY 16R/34L WAS CLOSED. THERE ARE NO INST APCHS PUBLISHED FOR RWY 34R SO A VISUAL APCH WAS REQUIRED. VISIBILITY WAS NOT RESTR BY WX; BUT APCH WOULD BE MADE IN DUSK LIGHTING CONDITIONS UNDER AN OVCST LAYER AT AROUND 17000 FT MSL. I HAD NOT LANDED TO THE N AT RNO PREVIOUSLY SO I WANTED TO USE ALL AVAILABLE AIDS. I WAS AWARE OF THE HIGH TERRAIN AT THIS ARPT AND WANTED TO BE PREPARED. I DISCUSSED THE ARR WITH THE CAPT AND I STUDIED THE 19-06 PAGE AND THE BACK COURSE LOC APCH TO RWY 34L EVEN THOUGH IT WOULD NOT BE USED. WE BUILT AN FMC VISUAL APCH WITH A 5 MI RWY EXTENSION POINT. I ASSIGNED AN ALT OF 6000 FT MSL TO THIS WAYPOINT TO ASSIST WITH VERT GUIDANCE. I CHOSE 6000 FT MSL FOR 2 REASONS: 1) IT PROVIDED A NORMAL 3 DEG GLIDE PATH TO THE RWY THRESHOLD AT 4408 FT MSL; AND 2) IT WAS COMPATIBLE WITH THE STEPDOWN ALTS ON THE ADJACENT BACK COURSE LOC RWY 34L APCH; WHICH ALLOWS A DSCNT OUT OF 6800 FT MSL TO 6000 FT MSL AT A DISTANCE OF 6.3 NM FROM THE THRESHOLD OF THAT RWY. I FLEW APCH WITH THE AUTOPLT ENGAGED AND COUPLED TO THE LNAV COURSE WITH THE INTENT TO DISCONNECT THE AUTOPLT JUST PRIOR TO THE RWY EXTENSION POINT. I USED VERT SPD TO MATCH THE FMC-COMPUTED DSCNT RATE. AT APPROX 10 MI FROM THE FIELD; I NOTED THE PAPI'S WERE VISIBLE IN THE DISTANCE BUT SHOWING MOSTLY RED. AT APPROX 7000 FT MSL; I RECEIVED A GPWS CAUTION OF 'TERRAIN; TERRAIN; PULL UP; PULL UP!' I DID NOT GET ANY GPWS WARNINGS FIRST (IE; 'CAUTION TERRAIN') AND THIS STRUCK ME AS ODD. OUTSIDE; I COULD SEE FINGER OF A RIDGE LINE EXTENDING ACROSS OUR FLT PATH; L TO R. I HAD SEEN THIS TERRAIN ALREADY; BUT HAD PROJECTED OUR FLT PATH TO BE FAR ENOUGH ABOVE IT THAT IT WOULD NOT BE A CONCERN. PERHAPS IN THE DUSK LIGHTING CONDITIONS; I HAD MISJUDGED THE PROX? UPON RECEIPT OF THE CAUTION; I THOUGHT ABOUT EXECUTING THE GPWS CAUTION TERRAIN AVOIDANCE MANEUVER. BUT I THOUGHT THAT THIS WOULD CERTAINLY LEAD TO US HAVING TO ABANDON THE APCH; AND I DID NOT WANT TO DO THAT FROM A VISUAL APCH IN MOUNTAINOUS TERRAIN WITH DARKNESS APCHING; ESPECIALLY SINCE NONE OF THE NAVAIDS REQUIRED TO FLY THE PUBLISHED MISSED APCH FOR THE ADJACENT RWY 34L BACK COURSE LOC WOULD BE AVAILABLE. IN ADDITION; I WAS IN DAY; VMC WITH A VISUAL ON THE TERRAIN THAT CAUSED THE CAUTION AND I FELT THAT I COULD SAFELY AVOID IT AND CONTINUE. AS A RESULT; I ELECTED TO DISCONNECT THE AUTOPLT; INCREASE PWR; AND INCREASE PITCH AS REQUIRED TO SILENCE THE CAUTION. THIS SEEMED TO BE THE LEAST RISKY COURSE OF ACTION AT THE TIME; BUT I REALIZE IN RETROSPECT THAT I DID NOT FOLLOW COMPANY PROC AS OUTLINED IN THE FOM AND PROBABLY SHOULD HAVE. I COULD SEE WE WERE CLR OF THE RIDGE LINE AND I THOUGHT IT WAS OK TO RESUME DSCNT; SO I RELAXED BACK PRESSURE ON THE STICK AND STARTED A DSCNT; ONLY TO GET A SECOND CAUTION ('PULL UP'). APPARENTLY; WE WERE STILL IN THE COMPUTER'S CAUTION ENVELOPE; EVEN THOUGH WE HAD NOTHING BUT THE VALLEY FLOOR BTWN US AND THE RWY NOW. I AGAIN INCREASED PWR AND PITCH TO CLB UNTIL THE CAUTION SILENCED. AFTER CLBING AND LEVELING OFF; I RESUMED THE APCH USING PAPI GUIDANCE AND LANDED UNEVENTFULLY ON RWY 34R. CONTRIBUTING FACTORS: MY UNFAMILIARITY WITH N APCHS AT RNO WAS A FACTOR. MY CHOICE OF 6000 FT MSL MAY HAVE BEEN TOO LOW FOR THE RWY EXTENSION POINT AT 5 MI. MY POOR XCHK LED TO DIPPING BELOW THE FMC-COMPUTED FLT PATH. MY PREMATURE DSCNT AFTER THE FIRST RECOVERY LED TO ANOTHER CAUTION. MY DECISION NOT TO ABANDON THE APCH AFTER THE FIRST CAUTION SUBJECTED ME TO A SECOND ONE. PREVENTION: OBVIOUSLY; I COULD HAVE DONE THINGS BETTER ON THIS APCH. I DID NOT STRICTLY ADHERE TO THE VERT PROFILE I HAD PLANNED IN THE FMC; AND A BETTER XCHK WILL PREVENT THAT IN THE FUTURE. BETTER ACFT EQUIP WOULD ALLOW USE OF THE CHARTED RNAV (GPS) APCH TO RWY 34R. THE -300'S AVIONICS ARE NOT COMPATIBLE WITH RNAV (GPS) APCHS; AND WHILE THE -700'S AVIONICS ARE PROBABLY CAPABLE; WE ARE PROHIBITED BY OPSSPECS FROM FLYING THESE KINDS OF APCHS.