Narrative:

We received a visual approach clearance from boi approach around 20 mi from the field and at 8000 ft MSL. Clearance given was 'cleared visual approach runway 28R; maintain at or above 4500 ft MSL until 5 mi.' descending through 4600 ft MSL at approximately 6 mi from the runway and 1 mi south of extended runway centerline; we received a 'terrain; terrain' warning from the GPWS. I leveled off at 4550 ft MSL and noticed yellow; boxed terrain on the map display directly in front of and around our position. The radio altimeter showed approximately 1600 ft AGL. Though it was dark with limited ground visibility; we could see the outline of terrain to the right of the aircraft with which we had adequate altitude clearance. We received no further aural warning from the GPWS and I elected to climb approximately 200 ft. The captain queried approach control about our altitude versus the MVA; and approach reiterated that 'at or above 4500 ft MSL to 5 mi' was the correct clearance. The yellow; 'boxed' terrain on the map display disappeared after climbing approximately 150; and at that point I elected to configure the aircraft and the subsequent landing at boi was uneventful. The captain and I discussed the event upon landing and felt we should submit a report due to the possibility of another crew receiving this warning while performing a visual approach into boi. Not sure if GPWS database was off or if the altitude given was appropriate for the approach.

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Original NASA ASRS Text

Title: B737 FLT CREW REPORTS ANOMALOUS GPWS WARNING DURING RADAR VECTORS FOR A VISUAL APPROACH TO RWY 28R AT BOI.

Narrative: WE RECEIVED A VISUAL APCH CLRNC FROM BOI APCH AROUND 20 MI FROM THE FIELD AND AT 8000 FT MSL. CLRNC GIVEN WAS 'CLRED VISUAL APCH RWY 28R; MAINTAIN AT OR ABOVE 4500 FT MSL UNTIL 5 MI.' DSNDING THROUGH 4600 FT MSL AT APPROX 6 MI FROM THE RWY AND 1 MI S OF EXTENDED RWY CTRLINE; WE RECEIVED A 'TERRAIN; TERRAIN' WARNING FROM THE GPWS. I LEVELED OFF AT 4550 FT MSL AND NOTICED YELLOW; BOXED TERRAIN ON THE MAP DISPLAY DIRECTLY IN FRONT OF AND AROUND OUR POS. THE RADIO ALTIMETER SHOWED APPROX 1600 FT AGL. THOUGH IT WAS DARK WITH LIMITED GND VISIBILITY; WE COULD SEE THE OUTLINE OF TERRAIN TO THE R OF THE ACFT WITH WHICH WE HAD ADEQUATE ALT CLRNC. WE RECEIVED NO FURTHER AURAL WARNING FROM THE GPWS AND I ELECTED TO CLB APPROX 200 FT. THE CAPT QUERIED APCH CTL ABOUT OUR ALT VERSUS THE MVA; AND APCH REITERATED THAT 'AT OR ABOVE 4500 FT MSL TO 5 MI' WAS THE CORRECT CLRNC. THE YELLOW; 'BOXED' TERRAIN ON THE MAP DISPLAY DISAPPEARED AFTER CLBING APPROX 150; AND AT THAT POINT I ELECTED TO CONFIGURE THE ACFT AND THE SUBSEQUENT LNDG AT BOI WAS UNEVENTFUL. THE CAPT AND I DISCUSSED THE EVENT UPON LNDG AND FELT WE SHOULD SUBMIT A RPT DUE TO THE POSSIBILITY OF ANOTHER CREW RECEIVING THIS WARNING WHILE PERFORMING A VISUAL APCH INTO BOI. NOT SURE IF GPWS DATABASE WAS OFF OR IF THE ALT GIVEN WAS APPROPRIATE FOR THE APCH.

Data retrieved from NASA's ASRS site as of January 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.