Narrative:

The WX was 500 ft overcast, with tops at approximately 9000 ft MSL. This was an ILS approach into a mountain airport, elevation 5700 ft MSL. I was assigned the ILS DME 17 approach to mtj, via the 14.8 DME arc. I entered the arc from V-26, as depicted, began flying the arc, and descended to 9500 ft MSL, the correct altitude for that segment. I tuned navigation #1 to the ILS frequency and verified the identify. After several mins on the arc, the CDI had not come in. Upon checking navigation #2, I realized that I had gone through the localizer by perhaps 1 mi. Fortunately, we were above the cloud deck and could see all surrounding terrain. Thus, we were simply able to rejoin the proper course and fly an uneventful ILS. However, had we been in IMC on the arc, we could have been in serious danger, given the terrain in the area. The reason that the CDI did not come in, was that it was set to receive its signal from my LORAN, as opposed to navigation #1. On one level, this problem could have been avoided simply by switching my CDI to receive navigation #1, instead of my LORAN. However, in a more important sense, I see this problem as one of procedure. What I need to do is develop a procedure to ensure the proper CDI setting on every approach. There are 2 ways I can (and intent) to do this in the future. First, I will add 'CDI input -- set' to my approach checklist. Second, I will add to my mental checklist to switch my CDI any time I tune in an approach frequency. (I can doublechk this by rotating my obs to ensure that the CDI changes as I do, which it does not when tuned to my LORAN.) another thing I can to do avoid a problem like this on a DME arc in the future -- or at least detect it more quickly -- is to follow my progress along the arc more closely on navigation #2. This approach has a turn-in radial of 341 degrees, anticipating an approach along the 348 degree radial from mtj. I had tuned my navigation #2 to center on this radial, but did not look at this until I had passed the turn in. So when navigation #2 did not center, I simply expected it to center -- without realizing for some time that it was not going to center. I realized my mistake only when I centered the CDI on my navigation #2 and realized I was past the turn-in to the localizer. Had I been ctring and re-ctring my navigation #2 CDI constantly as I flew along the DME arc, I would have realized where I was along the arc at all times. Instead of only at the turn in point, and would not need to rely as much on the localizer to let me know when to turn in. This is basic instrument procedure.

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Original NASA ASRS Text

Title: A C340 PLT DID NOT EXECUTE THE DME ARC PROPERLY AT MTJ.

Narrative: THE WX WAS 500 FT OVCST, WITH TOPS AT APPROX 9000 FT MSL. THIS WAS AN ILS APCH INTO A MOUNTAIN ARPT, ELEVATION 5700 FT MSL. I WAS ASSIGNED THE ILS DME 17 APCH TO MTJ, VIA THE 14.8 DME ARC. I ENTERED THE ARC FROM V-26, AS DEPICTED, BEGAN FLYING THE ARC, AND DSNDED TO 9500 FT MSL, THE CORRECT ALT FOR THAT SEGMENT. I TUNED NAV #1 TO THE ILS FREQ AND VERIFIED THE IDENT. AFTER SEVERAL MINS ON THE ARC, THE CDI HAD NOT COME IN. UPON CHKING NAV #2, I REALIZED THAT I HAD GONE THROUGH THE LOC BY PERHAPS 1 MI. FORTUNATELY, WE WERE ABOVE THE CLOUD DECK AND COULD SEE ALL SURROUNDING TERRAIN. THUS, WE WERE SIMPLY ABLE TO REJOIN THE PROPER COURSE AND FLY AN UNEVENTFUL ILS. HOWEVER, HAD WE BEEN IN IMC ON THE ARC, WE COULD HAVE BEEN IN SERIOUS DANGER, GIVEN THE TERRAIN IN THE AREA. THE REASON THAT THE CDI DID NOT COME IN, WAS THAT IT WAS SET TO RECEIVE ITS SIGNAL FROM MY LORAN, AS OPPOSED TO NAV #1. ON ONE LEVEL, THIS PROB COULD HAVE BEEN AVOIDED SIMPLY BY SWITCHING MY CDI TO RECEIVE NAV #1, INSTEAD OF MY LORAN. HOWEVER, IN A MORE IMPORTANT SENSE, I SEE THIS PROB AS ONE OF PROC. WHAT I NEED TO DO IS DEVELOP A PROC TO ENSURE THE PROPER CDI SETTING ON EVERY APCH. THERE ARE 2 WAYS I CAN (AND INTENT) TO DO THIS IN THE FUTURE. FIRST, I WILL ADD 'CDI INPUT -- SET' TO MY APCH CHKLIST. SECOND, I WILL ADD TO MY MENTAL CHKLIST TO SWITCH MY CDI ANY TIME I TUNE IN AN APCH FREQ. (I CAN DOUBLECHK THIS BY ROTATING MY OBS TO ENSURE THAT THE CDI CHANGES AS I DO, WHICH IT DOES NOT WHEN TUNED TO MY LORAN.) ANOTHER THING I CAN TO DO AVOID A PROB LIKE THIS ON A DME ARC IN THE FUTURE -- OR AT LEAST DETECT IT MORE QUICKLY -- IS TO FOLLOW MY PROGRESS ALONG THE ARC MORE CLOSELY ON NAV #2. THIS APCH HAS A TURN-IN RADIAL OF 341 DEGS, ANTICIPATING AN APCH ALONG THE 348 DEG RADIAL FROM MTJ. I HAD TUNED MY NAV #2 TO CTR ON THIS RADIAL, BUT DID NOT LOOK AT THIS UNTIL I HAD PASSED THE TURN IN. SO WHEN NAV #2 DID NOT CTR, I SIMPLY EXPECTED IT TO CTR -- WITHOUT REALIZING FOR SOME TIME THAT IT WAS NOT GOING TO CTR. I REALIZED MY MISTAKE ONLY WHEN I CTRED THE CDI ON MY NAV #2 AND REALIZED I WAS PAST THE TURN-IN TO THE LOC. HAD I BEEN CTRING AND RE-CTRING MY NAV #2 CDI CONSTANTLY AS I FLEW ALONG THE DME ARC, I WOULD HAVE REALIZED WHERE I WAS ALONG THE ARC AT ALL TIMES. INSTEAD OF ONLY AT THE TURN IN POINT, AND WOULD NOT NEED TO RELY AS MUCH ON THE LOC TO LET ME KNOW WHEN TO TURN IN. THIS IS BASIC INST PROC.

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.