DC9 FO BELIEVES THAT HE DSNDED TOO EARLY AFTER BEING CLRED FOR THE APCH SINCE HE WAS OUTSIDE OF THE PUBLISHED APCH FIX AND THEREFORE; NOT ESTABLISHED ON THE APCH BEFORE DSNDING AS CLRED.

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ON VECTORS FOR A LOW APCH; WE WERE INSTRUCTED 'MAINTAIN 4000 FT UNTIL ESTABLISHED; CLRED FOR THE APCH.' WE WERE ESTABLISHED INBOUND ON THE LOC AT 19 DME. THE FIRST DME FIX IS AT 15 DME. THE MINIMUM ALT AT THAT FIX IS 3000 FT. SINCE ESTABLISHED; THE CAPT SAW MINIMUM ALT 3000 FT AND DIALED IN 3000 FT AND STATED CLRED TO 3000 FT. I STARTED DOWN TO 3000 FT ABOUT 2 MI OUTSIDE THE FIX. WE COMPLETED THE APCH AND LNDG UNEVENTFULLY. I AGAIN REVIEWED THE APCH ON THE GND; AND HAVE CONCLUDED THAT EVEN THOUGH WE WERE INBOUND ON THE LOC; WE WERE OUTSIDE THE FIRST DME FIX; THUS; NOT ON A 'PUBLISHED PORTION' OF THE APCH. I SHOULD HAVE REQUESTED 3000 FT WITH ATC OR WAITED UNTIL I CROSSED THE INITIAL DME FIX BEFORE DSNDING. (THOUGHT WE WOULD BE HIGH.) THE APCH HAD NO TRANSITION; PROC TURN; OR TIMED HOLD; JUST THE INITIAL DME FIX. THE CTLR GAVE A HIGHER ALT THAN THE INITIAL APCH ALT; AND THE MANY TIMES WE LOOK AT THAT INITIAL ALT INBOUND (WHICH IS NORMALLY CORRECT; IE; WITHIN 10 MI) ALL LED TO THE SELECTION OF THE DSCNT TO 3000 FT PRIOR TO THE FIX.