SMA PLT ON APCH USES GPS FOR DISTANCE BUT HAS IT SET ON VOR INSTEAD OF ARPT. BELIEVING HE HAS A FALSE GS HE DSNDS. HE IS GIVEN A LOW ALERT BY THE CTLR. A GAR FOLLOWS WITH SECOND APCH CORRECT.

Narrative

I USED THE GPS FOR DISTANCE INFO WHEN IT WAS SET FOR THE VOR INSTEAD OF THE ARPT. THINKING THAT I WAS TOO HIGH AND HAVING A 'FALSE' GS I DSNDED UNDER THE MINIMUM ALT. BEING 1.5-2 MI FROM THE VOR BUT THINKING IT'S THE ARPT I DSNDED DOWN TO 1000 FT. I WAS SUPPOSED TO STAY AT 1400 FT UNTIL REACHING THE VOR. ATC ADVISED OF LOW ALT. I MADE A GAR AND CHANGED THE GPS FOR THE ARPT INSTEAD. AND I USED THE DME FOR DISTANCE INFO WHICH I SHOULD HAVE DONE IN THE FIRST PLACE. THE SECOND APCH WENT WITHOUT ANY PROBS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT HE FELT VERY EMBARRASSED WHEN HE REALIZED HIS ERROR. HE JUST KNEW THINGS WERE NOT RIGHT ON THE FIRST APCH AND HAD TO REVIEW HIS PROCS TO DISCOVER THE PROB. HE IS VERY PLEASED WITH GPS USE AND FEELS IT IS VERY HELPFUL FOR NAV AND VERY PRECISE. IT HAD MALFUNCTIONED TWICE WHEN THERE WAS HVY RAIN AND STATIC ALONG WITH TURB. THE CARD WAS REMOVED; CLEANED AND REPLACED INFLT THEN WORKED OK. THE ACFT IS IN FOR AN ANNUAL CURRENTLY AND HE HAS REQUESTED A CHK OF THE GPS.