PIPER PA30 TWIN COMMANCHE; CAUSED A LOW ALT ALERT FROM APCH CTL DURING A GPS APCH. RPTR WONDERED IF EVERYONE WOULD RECEIVE AN ALERT AND WHY THE DIFFERENCE IN THE PROFILE DEPICTION OF THE APCH DSCNT BTWN THE COMMERCIAL AND THE NOAA APCH CHARTS.

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APCHING OLV ON (NDB) OR GPS APCH RWY 36; FLYING THE GPS APCH. ESTABLISHED INBOUND 2000 FT AND PASSED 6 MI FROM EHAGO INTXN; STARTED DSCNT TO MDA 1080 FT. AT APPROX 1500 FT APCH EXCITEDLY INFORMED ME OF A LOW ALT ALERT AND TO STOP DSCNT IMMEDIATELY. I STOPPED DSCNT UNTIL I WAS NOTIFIED ALT ALERT STOPPED. CONTINUED APCH; BROKE OUT OF CLOUDS AND CANCELED IFR; PROCEEDED VISUALLY. IN REVIEWING THE COMMERCIAL CHART PLATE IT SHOWS DSCNT FROM 2000 FT WITHIN 10 NM APPLICABLE AND THE PROFILE VIEW SHOWS YOU SHOULD BE LEVEL AT MINIMUMS BEFORE EHAGO. THIS IS WHAT I WAS DOING. WILL THERE ALWAYS BE A LOW ALT ALERT WHEN SHOOTING THE APCH AS PUBLISHED? AN INTERESTING OBSERVATION: THE COMMERCIAL CHART PROFILE VIEW DEPICTS YOU SHOULD BE LEVEL AT MINIMUMS BEFORE EHAGO WHILE COMPARED TO THE GOV CHARTS THEY DO NOT DEPICT THIS BUT A DSCNT (CONSTANT) THROUGH EHAGO. WHY THE DIFFERENCE? CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT HE HAD MADE THIS APCH SEVERAL TIMES IN THE PAST AND HAD NEVER HAD A LOW ALT ALERT. HE SUGGESTED THAT IT MIGHT BE BECAUSE HE WAS HELD HIGH PRIOR TO APCH CLRNC CAUSING HIM TO ESTABLISH A HIGHER RATE OF DSCNT FURTHER OUT IN THE PROC TURN LIMITS. HE WAS ADVISED THAT THE APCH DSCNT CHART DEPICTIONS ARE NOT TO SCALE AND ARE JUST A VISUAL REF TO MAKE A NON PRECISION DSCNT TO THE MDA PRIOR TO THE ARPT.