Narrative:

As I was being vectored on descent to slc on an IFR flight plan from 7s0 (ronan, mt), I was cleared to descend to 12000 ft MSL and vectored on a course of approximately 150 degrees to intercept the localizer to runway 17 at slc. I was between 15-20 mi north of the airport, and when I switched my navigation radio to the localizer frequency, it was flagged, I informed the controller I was not receiving the signal and tuned my other navigation receiver to the localizer. While I was distraction by the radio problem, I descended to 11600 ft (approximately), which was 400 ft below the assigned altitude. The controller then informed me of the altitude problem, and I immediately climbed to 12000 ft MSL. The WX was clear, with ogden, ut, and slc to the south, along my path of flight, and the wasatch mountains to the east and north of my position. As I pulled up, I noticed I could see the ridge of the range out my left window, and I estimated I was 2000 ft above the highest terrain. This was, however, below IFR minimum altitude for this position. The approach controller asked me to call TRACON upon landing. The approach control supervisor informed me that my deviation in altitude put me too close to the terrain for IFR flight. The power output of the localizer transmitter may have been low, or my primary receiver may need to be checked. Just before the controller informed me of my deviation, the localizer signal was correctly received, indicating I was just out of range of the signal when the event occurred. The supervisor informed me that since I was close to terrain, the incident would be reported for possible further investigation.

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Original NASA ASRS Text

Title: AN AEROSTAR 601 PLT INADVERTENTLY DSNDS 400 FT BELOW ASSIGNED ALT IN MOUNTAINOUS TERRAIN.

Narrative: AS I WAS BEING VECTORED ON DSCNT TO SLC ON AN IFR FLT PLAN FROM 7S0 (RONAN, MT), I WAS CLRED TO DSND TO 12000 FT MSL AND VECTORED ON A COURSE OF APPROX 150 DEGS TO INTERCEPT THE LOC TO RWY 17 AT SLC. I WAS BTWN 15-20 MI N OF THE ARPT, AND WHEN I SWITCHED MY NAV RADIO TO THE LOC FREQ, IT WAS FLAGGED, I INFORMED THE CTLR I WAS NOT RECEIVING THE SIGNAL AND TUNED MY OTHER NAV RECEIVER TO THE LOC. WHILE I WAS DISTR BY THE RADIO PROB, I DSNDED TO 11600 FT (APPROX), WHICH WAS 400 FT BELOW THE ASSIGNED ALT. THE CTLR THEN INFORMED ME OF THE ALT PROB, AND I IMMEDIATELY CLBED TO 12000 FT MSL. THE WX WAS CLR, WITH OGDEN, UT, AND SLC TO THE S, ALONG MY PATH OF FLT, AND THE WASATCH MOUNTAINS TO THE E AND N OF MY POS. AS I PULLED UP, I NOTICED I COULD SEE THE RIDGE OF THE RANGE OUT MY L WINDOW, AND I ESTIMATED I WAS 2000 FT ABOVE THE HIGHEST TERRAIN. THIS WAS, HOWEVER, BELOW IFR MINIMUM ALT FOR THIS POS. THE APCH CTLR ASKED ME TO CALL TRACON UPON LNDG. THE APCH CTL SUPVR INFORMED ME THAT MY DEV IN ALT PUT ME TOO CLOSE TO THE TERRAIN FOR IFR FLT. THE PWR OUTPUT OF THE LOC XMITTER MAY HAVE BEEN LOW, OR MY PRIMARY RECEIVER MAY NEED TO BE CHKED. JUST BEFORE THE CTLR INFORMED ME OF MY DEV, THE LOC SIGNAL WAS CORRECTLY RECEIVED, INDICATING I WAS JUST OUT OF RANGE OF THE SIGNAL WHEN THE EVENT OCCURRED. THE SUPVR INFORMED ME THAT SINCE I WAS CLOSE TO TERRAIN, THE INCIDENT WOULD BE RPTED FOR POSSIBLE FURTHER INVESTIGATION.

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.