Narrative:

A gulfstream 3 entered my sector from the north of an IFR flight plan. I was working the radar associate position (the radar position was also staffed). About 60 mi north of flagstaff VOR (flg) the aircraft was told to descend to 15000 ft (mia). The aircraft was then told to turn left, direct to frisy intersection (IAF) and then to fly the ILS 21 approach to flg. The aircraft was also cleared to cross frisy at or above an altitude which was safe for terrain. Aircraft was told to report frisy intersection inbound so the controller could switch communications to flg tower. Pilot reported frisy intersection about 2 mi to the north and was given communication change to tower. While monitoring aircraft's progress inbound both controllers noticed the G3 continuing a northwest turn into high mountainous terrain. The aircraft was instructed through the tower by the radar associate controller to turn right immediately and climb to 15000 ft. The aircraft was then vectored back to a heading and told to proceed direct frisy intersection and report overhead. The pilot reported over frisy when he was 10 NM north of the intersection and tracking 40-50 degrees off course. I don't feel pilot error was to blame! 2 more aircraft that day (that I am aware of) also reported extreme NAVAID fluctuations and wrong approach course guidance. I feel the approach is unsafe because of close proximity to terrain and wrong instrument guidance reported by pilots.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 2007 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.