ACR LGT; IN A NIGHT OP; WAS SAVED FROM IMPACTING ON DESIGNATED MOUNTAINOUS TERRAIN BY THE GPWS WHILE ON A VISUAL APCH TO 28R MILL VISUAL APCH TO PDX; OR.

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FLT SEA TO PDX ON HELNS 2 ARR TO PDX. AFTER KALMA; PDX APCH VECTORED US APPROX HDG 140 FOR SPACING FOR INBOUND ACFT FROM THE S; AND FOR DOWNWIND/BASE FOR THE MILL VISUAL APCH. WE WERE A LITTLE FURTHER THAN USUAL ABEAM THE ARPT; PROBABLY FOR ANTICIPATED SPACING. IT WAS A CRYSTAL CLR NIGHT AND WE WERE LEVEL AT 6000 FT MSL. APPROX XING V448 WE RPTED ARPT AND MILL IN SIGHT AND WERE CLRED FOR THE MILL VISUAL RWY 28R APCH. THE AREA BELOW US WAS LIKE A 'BLACK HOLE' BECAUSE OF FOREST AND IT BEING UNPOPULATED. THE CITY LIGHTS/ARPT WERE OFF OUR R WING -- A BEAUTIFUL NIGHT. AFTER BEING CLRED FOR THE VISUAL; I BEGAN DSCNT SO AS TO ARRIVE OVER THE MILL AT THE RECOMMENDED 3000 FT MSL. AT APPROX XING OF V112 AT 4100 FT MSL THE GPWS WENT 'WHOOP! WHOOP! PULL UP! TERRAIN!' FOR A SPLIT SECOND WE THOUGHT IT WAS A FALSE WARNING SINCE WE WERE STILL LOOKING AT THE ARPT/CITY. THEN I NOTICED BOTH RADIO ALTIMETERS GO FROM 2500 FT TO 400 FT IN ABOUT 1-2 SECONDS. I IMMEDIATELY APPLIED FULL PWR AND INITIATED A MAX CLB UNTIL OVER THE CITY'S OUTSKIRTS (LIGHTS). THEN I CONTINUED THE DSCNT/VISUAL APCH AND LANDED. OUR WHOLE CREW SERVES PDX DAILY AND KNOWS THE ARPT WELL. SIMPLE FACT IS THAT MOST PLTS GOING INTO A FAMILIAR ARPT USE THE APCH PLATE AND DO NOT OFTEN REFER TO THE AREA CHART. APCH CTL WAS WORKING OTHER ACFT AND DID NOT CALL US ABOUT BEING TOO LOW. HE TURNED US OVER TO TWR AROUND THE MILL. ALTHOUGH WE SCREWED UP AND LEARNED OUR LESSON; IT MAY BE PRUDENT TO PUBLISH WARNINGS FOR NIGHT VISUALS ON THE 19-1 APCH PLATE (MILL VISUAL) AND AT LEAST PUT THE MSA 'PIE' BACK ON THE TOP OF THAT CHART. WE WERE STUPID; AND VERY LUCKY.