Narrative:

Sel instrument rated pilot on IFR cross county flight from sna to sba with cfii aboard. Flight under the hood progressed well until partial panel work was introduced into the flight approximately 30 NM east of sba. Approach notified us to expect ILS runway 7 into sba and I notified him we would make a localizer only approach into sba. Radar vectors and the intercept took us onto the localizer. At that point, I was working with the attitude indicator, the #1 navigation, and the GS failed (all simulated). Establishing myself on the localizer (075 degree) with the #2 navigation, I then changed frequency to gvo 113.8 and set the needle to 188 degree to establish the FAF (napps intersection) for the step down descent. The problem here of course is that the proper radial from gvo is 118 degree thinking I had passed napps intersection I started to descend to the MDA altitude. Approach then issued a low altitude warning and we quickly ascended back to proper altitude. The workload on this partial panel approach evidently was enough that I didn't catch my error of 188 vs 118 radial. Needless to say, I will be much more careful on future flts to verify the radials I set in.

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Original NASA ASRS Text

Title: LOW ALT ALERT SYS (MSAW) TRIGGERED AS INST RATED PLT AND CFII ON INST TRAINING FLT TO SBA DSNDS TO MDA PREMATURELY DUE MISSET VOR RADIAL FOR NAPPS INTXN.

Narrative: SEL INST RATED PLT ON IFR CROSS COUNTY FLT FROM SNA TO SBA WITH CFII ABOARD. FLT UNDER THE HOOD PROGRESSED WELL UNTIL PARTIAL PANEL WORK WAS INTRODUCED INTO THE FLT APPROX 30 NM E OF SBA. APCH NOTIFIED US TO EXPECT ILS RWY 7 INTO SBA AND I NOTIFIED HIM WE WOULD MAKE A LOC ONLY APCH INTO SBA. RADAR VECTORS AND THE INTERCEPT TOOK US ONTO THE LOC. AT THAT POINT, I WAS WORKING WITH THE ATTITUDE INDICATOR, THE #1 NAV, AND THE GS FAILED (ALL SIMULATED). ESTABLISHING MYSELF ON THE LOC (075 DEG) WITH THE #2 NAV, I THEN CHANGED FREQ TO GVO 113.8 AND SET THE NEEDLE TO 188 DEG TO ESTABLISH THE FAF (NAPPS INTXN) FOR THE STEP DOWN DSCNT. THE PROBLEM HERE OF COURSE IS THAT THE PROPER RADIAL FROM GVO IS 118 DEG THINKING I HAD PASSED NAPPS INTXN I STARTED TO DSND TO THE MDA ALT. APCH THEN ISSUED A LOW ALT WARNING AND WE QUICKLY ASCENDED BACK TO PROPER ALT. THE WORKLOAD ON THIS PARTIAL PANEL APCH EVIDENTLY WAS ENOUGH THAT I DIDN'T CATCH MY ERROR OF 188 VS 118 RADIAL. NEEDLESS TO SAY, I WILL BE MUCH MORE CAREFUL ON FUTURE FLTS TO VERIFY THE RADIALS I SET IN.

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.