Narrative:

I was the PF during our approach into boi at night to runway 28R. Approach vectored us for a right downwind to runway 28R stepping us down through the mountains. They turned us on a 10 mi base and told us to 'descend to 4500 ft; maintain 4500 ft until established; cleared the visual to runway 28R.' we had not called the field in sight yet and we told ATC we didn't have it yet. I quickly looked for the runway and picked it up as we were approaching final. Approach then asked if we had the field in sight and we told them we did. They reissued the clearance for the visual at 4500 ft until established. While on final; slightly right of course; approximately 10 mi from the field descending through 5000 ft; we received a ground proximity warning to pull up. I immediately initiated the terrain avoidance maneuver and climbed until the warning stopped (approximately 5500 ft). After clear of terrain and referring to the terrain display; we re-established the visual approach and landed uneventfully. After landing; we called tower to let them know what had happened. They said this happened quite often and approach was reviewing their procedures to try to prevent this from happening. They did say; however; that once we accepted clearance for the visual approach; ATC is no longer responsible for terrain separation. Several factors contributed to this error: pressure from ATC to accept the visual to a runway that had no precision approach; our false assumption that the altitude clearance of 4500 ft from ATC provided terrain clearance; and not seeing the terrain due to night conditions all contributed to the event. Thankfully; the ground proximity helped to break the error chain and worked as advertised. Don't accept clearance for the visual -- especially at night -- until you are sure you not only have the field in sight; but also that you are aware of all terrain/obstacle threats. ATC could advise that the 4500 ft restr is for noise abatement and does not provide terrain clearance.

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Original NASA ASRS Text

Title: MLG FLIGHT CREW EXPERIENCES GPWS TERRAIN WARNING WHILE FLYING NIGHT VISUAL TO RWY 28R AT BOI.

Narrative: I WAS THE PF DURING OUR APCH INTO BOI AT NIGHT TO RWY 28R. APCH VECTORED US FOR A R DOWNWIND TO RWY 28R STEPPING US DOWN THROUGH THE MOUNTAINS. THEY TURNED US ON A 10 MI BASE AND TOLD US TO 'DSND TO 4500 FT; MAINTAIN 4500 FT UNTIL ESTABLISHED; CLRED THE VISUAL TO RWY 28R.' WE HAD NOT CALLED THE FIELD IN SIGHT YET AND WE TOLD ATC WE DIDN'T HAVE IT YET. I QUICKLY LOOKED FOR THE RWY AND PICKED IT UP AS WE WERE APCHING FINAL. APCH THEN ASKED IF WE HAD THE FIELD IN SIGHT AND WE TOLD THEM WE DID. THEY REISSUED THE CLRNC FOR THE VISUAL AT 4500 FT UNTIL ESTABLISHED. WHILE ON FINAL; SLIGHTLY R OF COURSE; APPROX 10 MI FROM THE FIELD DSNDING THROUGH 5000 FT; WE RECEIVED A GND PROX WARNING TO PULL UP. I IMMEDIATELY INITIATED THE TERRAIN AVOIDANCE MANEUVER AND CLBED UNTIL THE WARNING STOPPED (APPROX 5500 FT). AFTER CLEAR OF TERRAIN AND REFERRING TO THE TERRAIN DISPLAY; WE RE-ESTABLISHED THE VISUAL APCH AND LANDED UNEVENTFULLY. AFTER LNDG; WE CALLED TWR TO LET THEM KNOW WHAT HAD HAPPENED. THEY SAID THIS HAPPENED QUITE OFTEN AND APCH WAS REVIEWING THEIR PROCS TO TRY TO PREVENT THIS FROM HAPPENING. THEY DID SAY; HOWEVER; THAT ONCE WE ACCEPTED CLRNC FOR THE VISUAL APCH; ATC IS NO LONGER RESPONSIBLE FOR TERRAIN SEPARATION. SEVERAL FACTORS CONTRIBUTED TO THIS ERROR: PRESSURE FROM ATC TO ACCEPT THE VISUAL TO A RWY THAT HAD NO PRECISION APCH; OUR FALSE ASSUMPTION THAT THE ALT CLRNC OF 4500 FT FROM ATC PROVIDED TERRAIN CLRNC; AND NOT SEEING THE TERRAIN DUE TO NIGHT CONDITIONS ALL CONTRIBUTED TO THE EVENT. THANKFULLY; THE GND PROX HELPED TO BREAK THE ERROR CHAIN AND WORKED AS ADVERTISED. DON'T ACCEPT CLRNC FOR THE VISUAL -- ESPECIALLY AT NIGHT -- UNTIL YOU ARE SURE YOU NOT ONLY HAVE THE FIELD IN SIGHT; BUT ALSO THAT YOU ARE AWARE OF ALL TERRAIN/OBSTACLE THREATS. ATC COULD ADVISE THAT THE 4500 FT RESTR IS FOR NOISE ABATEMENT AND DOES NOT PROVIDE TERRAIN CLRNC.

Data retrieved from NASA's ASRS site as of May 2009 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.