WRONG ALTIMETER SETTING PLACES AN MD90 1000 FT TOO LOW IN A NIGHT OP IN PROX OF DESIGNATED MOUNTAINOUS TERRAIN. TECHNICALLY A CFTT INCIDENT. ALTDEV ALT OVERSHOT IN DSCNT.

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APCHING FL180 DURING DSCNT TO LOWER ALT; I ASKED FO FOR ALTIMETER SETTING AND DSCNT CHKLIST. HE SAID IT WAS 30.43. MY FIRST THOUGHT WAS IT WAS PRETTY HIGH BUT THEN WE ENCOUNTERED CONTINUOUS LIGHT; OCCASIONAL MODERATE TURB. MY THOUGHTS TURNED TOWARD GETTING A SMOOTHER RIDE. ALL APPEARED NORMAL UNTIL WE LEVELED OFF AT 6000 FT MSL. APCH CTLR STATED WE WERE CLRED TO 6000 FT MSL. WE QUERIED HIM FOR THE ALTIMETER SETTING WHICH HE STATED WAS 29.43 VERSUS THE 30.43 WE HAD SET IN. THEREFORE; WE IN FACT WERE AT 5000 FT MSL; NOT 6000 FT MSL AS WE THOUGHT. AN IMMEDIATE CLB TO 6000 FT MSL WAS INITIATED IN VMC CONDITIONS FOLLOWED BY AN UNEVENTFUL LNDG. THE FO STATED HE HAD WRITTEN DOWN THE CORRECT ALTIMETER SETTING OF 29.43 BUT VERBALLY RPTED IT TO ME AS 30.43. I BELIEVE I WASN'T PERSISTENT ENOUGH IN FOLLOWING UP ON MY INITIAL FEELING THAT 30.43 WAS PRETTY HIGH. I ALLOWED MYSELF TO BECOME DISTR BY THE TURB WE WERE ENCOUNTERING. SUPPLEMENTAL INFO FROM ACN 355484: DURING DSCNT PHASE INTO BIL; FO OBTAINED AND WROTE DOWN A CORRECT BAROMETRIC PRESSURE FOR BIL ARPT OF 29.43. THIS WAS ALSO SET INTO THE OVERHEAD PRESSURE CTLR. THE ARPT WAS APPROX 12-15 MI AWAY AND VISIBLE.