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.

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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.