A DH8 FLC DSNDS TOWARDS HIGHER TERRAIN AFTER BEING CLRED FOR THE VISUAL APCH DURING A NIGHT OP. PIC WAS NOT FOLLOWING ANY PUBLISHED APCH PROCS WHILE 10-15 MI E OF ROA; VA.

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I DON'T THINK THAT THIS IS A POTENTIAL VIOLATION; IT COULD HAVE BEEN AN EQUIP MALFUNCTION; BUT IT DEFINITELY WAS AN 'I'M NEVER GOING TO DO THAT AGAIN.' I WAS CLRED FOR A VISUAL APCH INTO RWY 24 AT ROA ABOUT 15 MI OUT AND I WAS ON A 270 DEG HDG. IT WAS A VERY CLR; VERY DARK NIGHT. THE HILLS E OF ROA WERE JUST BLACK SPOTS ON THE SURFACE AND I COULD NOT TELL WHERE THE TOPS OF THE HILLS WERE. I HAVE FLOWN INTO ROA SEVERAL TIMES AND PRETTY MUCH KNEW WHERE THE HILLS WERE PLUS THE FO AND MYSELF HAD BEEN WATCHING THE TERRAIN AND COMPARING IT TO THE APCH PLATE AND THE ROADS ON THE GND. I WAS MAKING A VERY GRADUAL DSCNT INTO A POS JUST E OF RWY 24 SO THAT I COULD TURN FOR A 2 MI FINAL. IT LOOKED LIKE I WAS ON A NORMAL APCH PATH BUT THERE IS NO VASI INTO RWY 24. AT ABOUT 10 MI OUT I NOTICED THE RADAR ALTIMETER START DECREASING PRETTY FAST AND I LOOKED OUT TO MAKE SURE WE WERE AWAY FROM THE HILLS AND EVERYTHING LOOKED GOOD. THEN THE GPWS STARTED SAYING 'TERRAIN.' WHEN I LOOKED BACK AT THE RADAR ALT AGAIN IT SAID 1080 FT. I ADDED PWR; PITCHED UP; AND LOOKED AT THE RADAR ALT AGAIN AND IT SAID 1800 FT. THE GPWS CONTINUED TO SCREAM AND AFTER ABOUT 3 MORE TIMES OF HEARING 'TERRAIN' I THOUGHT THAT THIS WAS SILLY AND I'M SCARING THE PEOPLE FOR NO REASON. I PUNCHED THE RED LIGHT AND TURNED IT OFF AND CONTINUED FOR A NORMAL APCH AND LNDG. A FEW DAYS LATER I FLEW INTO ROA DURING THE DAY AND TOOK A GOOD LOOK AT THE SIT AND FOLLOWED THE VOR DME APCH IN VISUAL CONDITIONS. I COULDN'T TELL WHAT SET OFF THE GPWS FROM BEFORE BUT I FELT REAL SAFE GOING TO THE CLART INTXN AT 3700 FT AND DOING A VISUAL APCH FROM THAT POS. ALTHOUGH YOU CAN'T DSND FROM 2.8 DME INTO RWY 24; YOU CAN DO A NORMAL DSCNT FROM THE CLART INTXN AND THIS KEEPS YOU CLR OF THE HILLS. ALL OF MY VISUAL APCHS INTO 'MOUNTAINOUS' ARPTS WILL BE DONE IN THIS MANNER FROM NOW ON. WHICH MAKES ME THINK; WHY DOESN'T ATC HAVE A CLRNC THAT STATES 'CLRED FOR THE VISUAL VOR (ILS; ETC) APCH' WHERE APPROPRIATE!