PA24 PLT DSNDED BELOW THE MINIMUM ALT LISTED ON THE APCH CHART AT DWH.

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ON ARR IN THE HOUSTON TERMINAL AREA; APCH ASKED IF I WANTED A DIRECT VISUAL; OR THE APCH INTO DWH. I REPLIED THAT I WOULD LIKE TO 'FOLLOW THE LOC IN.' APCH THEN VECTORED AND CLRED ME FOR THE DWH LOC RWY 17R APCH. THE MINIMUM ALT ON THIS APCH IS 1800 FT UNTIL THE FAF AT 6 DME. WX WAS CAVU. I RPTED VISUAL ON DWH AT ABOUT 12 DME UPON JOINING THE LOC. APCH ALMOST IMMEDIATELY HANDED ME TO DWH TWR. I CONTACTED DWH TWR AND RPTED 'ON THE LOC.' DWH TWR IMMEDIATELY CLRED ME TO LAND. AT THIS POINT I WAS STILL ABOUT 8-10 DME OUT. HAVING DWH VISUAL UNDER TWR CTL IN CLASS E; I WAS IN POS FOR A NORMAL APCH AND LNDG. I THEREFORE BEGAN A GENTLE DSCNT TO 1500 FT (WHICH IS THE NORMAL LCL VFR APCH ALT FOR DWH RWY 17R). MY POS; BEING APPROPRIATE FOR A NORMAL APCH AND LNDG; COUPLED WITH CAVU VMC AND PROX TO THE FIELD DID NOT SEEM TO MANDATE COMPLETION OF THE FORMAL APCH PROC TO THE FAF. APCH CALLED THE TWR AND DISCUSSED MY DSCNT BELOW 1800 FT PRIOR TO THE 6 DME FAF FOR THE LOC RWY 17R APCH. I REPLIED TO THE EFFECT THAT 'I GUESS I HAD TAKEN SOME LIBERTY BECAUSE OF THE CONDITIONS.' MY UNDERSTANDING IS THAT DWH TWR INDICATED THEY HAD NO ISSUE; BUT THAT APCH WANTED TO CONFIRM I; IN FACT; KNEW THE CORRECT ALT WAS 1800 FT TO THE FAF AND THAT I SHOULD HAVE MAINTAINED THAT ALT. I ATTRIBUTE MY (APPARENT) CONFUSION REGARDING THE REQUIREMENT TO HOLD ALT TO THE EXTREMELY EARLY HDOF TO THE DWH TWR WHILE IN CLASS E SPACE COUPLED WITH THE CAVU CONDITIONS PROVIDING THE APPROPRIATE 'IN POS FOR A NORMAL LNDG' EVEN THOUGH I HAD NOT PASSED THE FAF. IT MIGHT HAVE BEEN APPROPRIATE FOR ME TO CANCEL IFR UPON HDOF TO THE TWR; BUT IN THE CONTEXT OF THE APCH AND LNDG SCENARIO; IT SEEMED REDUNDANT TO THE SIT. IN THE FUTURE; I WILL ENSURE COMPLETE FORMALITY PRIOR TO ANY DEV.