Narrative:

I was radar vectored to intercept the published radial for a VOR/DME 33 approach at sioux falls, sd. I had established myself on the published radial and been cleared for the approach. The VOR and DME were properly set and idented. Also set up was the LORAN to show a reference to the airport in addition to the published approach. This is VFR LORAN and I had tuned it to fsd for a reference only. I thought this would be helpful since the VOR was located off the field. The published approach called for descent to MDA beginning at the 10 DME fix (final approach fix). My mistake came when I began a descent to MDA beginning at approximately 12- 13 DME. This happened because I referenced the LORAN distance to the airport rather than the VOR/DME fix. The approach called for a descent from 2900 ft MSL at the final approach fix to 1920 ft MSL, the straight in MDA. At approximately 2200 ft MSL sioux falls approach came over the radio advising the minimum altitude 'in that area' is 2900 ft. I acknowledged with 'roger.' since I was now below the cloud layer and had 3-5 mi forward visibility, I remained at 2200 ft. I also saw then my mistake in range information and realized I was about 2 mi (11.5-12 DME) short of the FAF. No more was said by the approach controllers relating to this. I feel there are two main factors that led to this error. The first being workload. The majority of our trips are 2 pilot crew. Not that conditions were so difficult for the day except for considerable turbulence in the approach phase, but simply going back to a single pilot cockpit flow is somewhat difficult when it is seldom done. The second factor is the use of multiple navigation methods. It was just too easy to reference the LORAN distance to the airport and forget the VOR was offset from the field and therefore the DME and LORAN were reading distances to different references. I hope and pray I, nor anyone else, makes this type of error again.

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Original NASA ASRS Text

Title: ATX PLT GETS CONFUSED AS TO HIS DSCNT POINT ON A VOR DME APCH AND DSNDS EARLY, IN THE VICINITY OF A TWR, BASED ON AN IMPROPER LORAN REFERENCE VS DME REFERENCE. THE APCH CTLR CALLED THIS TO THE PLT'S ATTENTION. THE PLT STOPPED HIS DSCNT AT THAT ALT IN VMC CONDITIONS AND SUCCESSFULLY COMPLETED THE APCH.

Narrative: I WAS RADAR VECTORED TO INTERCEPT THE PUBLISHED RADIAL FOR A VOR/DME 33 APCH AT SIOUX FALLS, SD. I HAD ESTABLISHED MYSELF ON THE PUBLISHED RADIAL AND BEEN CLRED FOR THE APCH. THE VOR AND DME WERE PROPERLY SET AND IDENTED. ALSO SET UP WAS THE LORAN TO SHOW A REFERENCE TO THE ARPT IN ADDITION TO THE PUBLISHED APCH. THIS IS VFR LORAN AND I HAD TUNED IT TO FSD FOR A REFERENCE ONLY. I THOUGHT THIS WOULD BE HELPFUL SINCE THE VOR WAS LOCATED OFF THE FIELD. THE PUBLISHED APCH CALLED FOR DSCNT TO MDA BEGINNING AT THE 10 DME FIX (FINAL APCH FIX). MY MISTAKE CAME WHEN I BEGAN A DSCNT TO MDA BEGINNING AT APPROX 12- 13 DME. THIS HAPPENED BECAUSE I REFERENCED THE LORAN DISTANCE TO THE ARPT RATHER THAN THE VOR/DME FIX. THE APCH CALLED FOR A DSCNT FROM 2900 FT MSL AT THE FINAL APCH FIX TO 1920 FT MSL, THE STRAIGHT IN MDA. AT APPROX 2200 FT MSL SIOUX FALLS APCH CAME OVER THE RADIO ADVISING THE MINIMUM ALT 'IN THAT AREA' IS 2900 FT. I ACKNOWLEDGED WITH 'ROGER.' SINCE I WAS NOW BELOW THE CLOUD LAYER AND HAD 3-5 MI FORWARD VISIBILITY, I REMAINED AT 2200 FT. I ALSO SAW THEN MY MISTAKE IN RANGE INFO AND REALIZED I WAS ABOUT 2 MI (11.5-12 DME) SHORT OF THE FAF. NO MORE WAS SAID BY THE APCH CTLRS RELATING TO THIS. I FEEL THERE ARE TWO MAIN FACTORS THAT LED TO THIS ERROR. THE FIRST BEING WORKLOAD. THE MAJORITY OF OUR TRIPS ARE 2 PLT CREW. NOT THAT CONDITIONS WERE SO DIFFICULT FOR THE DAY EXCEPT FOR CONSIDERABLE TURB IN THE APCH PHASE, BUT SIMPLY GOING BACK TO A SINGLE PLT COCKPIT FLOW IS SOMEWHAT DIFFICULT WHEN IT IS SELDOM DONE. THE SECOND FACTOR IS THE USE OF MULTIPLE NAV METHODS. IT WAS JUST TOO EASY TO REFERENCE THE LORAN DISTANCE TO THE ARPT AND FORGET THE VOR WAS OFFSET FROM THE FIELD AND THEREFORE THE DME AND LORAN WERE READING DISTANCES TO DIFFERENT REFS. I HOPE AND PRAY I, NOR ANYONE ELSE, MAKES THIS TYPE OF ERROR AGAIN.

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.