CPR Y CFTT WHILE ON APCH.

Narrative

A GULFSTREAM 3 ENTERED MY SECTOR FROM THE N OF AN IFR FLT PLAN. I WAS WORKING THE RADAR ASSOCIATE POS (THE RADAR POS WAS ALSO STAFFED). ABOUT 60 MI N OF FLAGSTAFF VOR (FLG) THE ACFT WAS TOLD TO DSND TO 15000 FT (MIA). THE ACFT WAS THEN TOLD TO TURN L; DIRECT TO FRISY INTXN (IAF) AND THEN TO FLY THE ILS 21 APCH TO FLG. THE ACFT WAS ALSO CLRED TO CROSS FRISY AT OR ABOVE AN ALT WHICH WAS SAFE FOR TERRAIN. ACFT WAS TOLD TO RPT FRISY INTXN INBOUND SO THE CTLR COULD SWITCH COMS TO FLG TWR. PLT RPTED FRISY INTXN ABOUT 2 MI TO THE N AND WAS GIVEN COM CHANGE TO TWR. WHILE MONITORING ACFT'S PROGRESS INBOUND BOTH CTLRS NOTICED THE G3 CONTINUING A NW TURN INTO HIGH MOUNTAINOUS TERRAIN. THE ACFT WAS INSTRUCTED THROUGH THE TWR BY THE RADAR ASSOCIATE CTLR TO TURN R IMMEDIATELY AND CLB TO 15000 FT. THE ACFT WAS THEN VECTORED BACK TO A HDG AND TOLD TO PROCEED DIRECT FRISY INTXN AND RPT OVERHEAD. THE PLT RPTED OVER FRISY WHEN HE WAS 10 NM N OF THE INTXN AND TRACKING 40-50 DEGS OFF COURSE. I DON'T FEEL PLT ERROR WAS TO BLAME! 2 MORE ACFT THAT DAY (THAT I AM AWARE OF) ALSO RPTED EXTREME NAVAID FLUCTUATIONS AND WRONG APCH COURSE GUIDANCE. I FEEL THE APCH IS UNSAFE BECAUSE OF CLOSE PROX TO TERRAIN AND WRONG INST GUIDANCE RPTED BY PLTS.