FLT CREW OF FA10 FLYING VOR RWY 23 APCH TO APF DSND EARLY AND GET LOW ALT FROM APCH CTLR AND TERRAIN WARNING FROM TAWS.

Narrative

I WAS SERVING AS PF AND CAPT. WE HAD EXPECTED AND BRIEFED THE RNAV (GPS) APCH TO RWY 23. AS WE GOT CLOSER IN WE DISCOVERED FROM THE ATIS THAT THEY WERE USING THE VOR RWY 23 APCH INSTEAD. WE BRIEFED THAT APCH AND SET THE FREQ IN THE #1 NAV RADIO AND THE FINAL APCH COURSE IN THE HSI. OUR STANDARD OPERATING PROC IS TO BRIEF THE APCH TOGETHER BY REFERRING TO THE APCH CHART AND THEN FOR THE PNF TO RETAIN THE APCH CHART AND TO MONITOR THE APCH. AS WE WERE BEING VECTORED FOR THE APCH; I BECAME UNCOMFORTABLE WITH MY NAVIGATION AND ASKED THE PNF TO HAND ME THE APCH CHART. I THEN RETAINED THE APCH CHART. AS WE WERE BEING VECTORED TO INTERCEPT THE FINAL APCH COURSE FOR THE VOR RWY 23 APCH; THE CTLR SAID; 'CLRED FOR THE VOR 23 APCH; MAINTAIN 2000 FT UNTIL ESTABLISHED.' WE WERE ABOUT 15 MILES FROM THE ARPT WHEN I FINISHED THE TURN ONTO THE FINAL APCH COURSE AND THEN SAID; 'SET 500 FT (THE MDA) INTO THE ALT ALERTER.' THE PNF THEN SAID; 'I AM NOT SURE OF WHAT ALT WE CAN GO TO.' THEN HE WENT AHEAD AND SET 500 FT IN THE ALERTER AND SAID; 'I NEED TO CHK TO SEE HOW LOW WE CAN GO NOW.' SINCE I HAD THE APCH CHART FOR THE VOR APCH WE WERE EXECUTING; THE PNF STARTED LOOKING AT THE APCH CHART FOR THE GPS APCH; WHICH WE HAD DISPLAYED ON THE MFD; TO SEE IF IT WOULD TELL HIM HOW LOW WE COULD GO. ABOUT THIS TIME; I SAID; 'WE CAN GO TO 500 FT AS SOON AS WE ARE ESTABLISHED;' AND STARTED THE DSCNT TO 500 FT. SOON THEREAFTER WE GOT A LOW ALT ALERT FROM APCH CTL AND AT ABOUT THE SAME TIME OUR TAWS STARTED WARNING US ABOUT A TWR AHEAD. WE ADVISED APCH CTL WE WERE VISUAL (WHICH WE WERE) AND PULLED UP UNTIL THE TAWS QUIT ADVISING US ABOUT THE TWR. FACTORS IN THIS INCIDENT WERE THE DEP FROM OUR STANDARD OPERATING PROCS IN MY TAKING THE APCH CHART WHICH LEFT THE PNF NO WAY TO MONITOR THE APCH; AND A LACK OF A FINAL APCH FIX ON THE APCH WHICH MADE IT LESS CLEAR AS TO WHEN THE DSCNT TO THE MDA COULD BEGIN.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR ADVISED THEY WERE VECTORED FROM THE N AND CLRED FOR THE VOR RWY 23 APCH. RPTR WAS NOT SURE WHETHER THE CTLR STATED CLRED FOR A STRAIGHT IN APCH OR; SIMPLY; CLRED FOR THE VOR RWY 23 APCH. RPTR DID STATE THAT OTHER ACFT PRIOR TO THEIR ARR FLEW A STRAIGHT IN APCH AND ALSO; THAT THE WX AT THE FIELD WAS VMC ALTHOUGH THERE WAS A LAYER OF CLOUDS THAT MADE UNINTERRUPTED VISION OF THE ARPT DIFFICULT UNTIL BELOW ABOUT 700 FT. RPTR FELT THE STRAIGHT IN COULD BE UTILIZED AND THAT THE 10 MILE LIMIT WITHIN WHICH THE PROC IS CHARTED WOULD ALLOW A DSCNT TO BEGIN ONCE INSIDE OF 10 MILES. THEY FELT THEIR ERROR WAS BEGINNING THE DSCNT UPON ESTABLISHING ON THE 055 DEG RADIAL; BUT PRIOR TO BEING WITHIN 10 MILES WAS THE CAUSE OF THE ALERTS. RPTR STATED; HOWEVER; THAT THAT APCH CLRNC WAS QUITE SPECIFIC THAT 2000 FT MSL BE MAINTAINED ONLY UNTIL ESTABLISHED INBOUND.