ALTDEV ALT EXCURSION AS ACR PIC DSNDS MLG BELOW LOM XING ALT PRIOR TO LOM ON A VISUAL APCH. CFIT. MSAW ALERT.

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WITH GOOD VFR CONDITIONS WE RPTED THE ARPT IN SIGHT AND WERE CLRED FOR A VISUAL APCH TO RWY 4. AT THIS TIME WE WERE ABOUT 20 NM OUT AND SLIGHTLY HIGH ON THE GS. THE LAST ALT ASSIGNED WAS 4000 FT. THE CAPT SET 2300 FT IN THE ALT; CONTINUED HIS DSCNT BELOW THE GS TO 2300 FT; AND LEVELED OFF TO SLOW TO APCH SPD. I SHOULD HAVE QUESTIONED HIS CHOICE OF ALT BECAUSE HE WAS STILL OUTSIDE OF CYE NDB. THERE ARE ANTENNAS AND RIDGES BTWN 2000 FT AND 2949 FT AND THE APCH CALLS FOR 3900 FT UNTIL CYE. WE HAD THE ANTENNAS VISUALLY BUT LOOKING BACK WE SHOULD HAVE OPERATED MORE CONSERVATIVELY. I SHOULD HAVE POINTED OUT TO THE CAPT THAT THERE ARE OBSTRUCTIONS TO CONSIDER. AND I SHOULD HAVE DONE THIS DURING THE APCH BRIEFING PORTION OF THE PRELIMINARY LNDG CHKLIST. ALSO; THE FACT THAT THIS APCH HAS 2 NDB'S SHOULD HAVE BEEN BORNE OUT IN THE BRIEFING TO ELIMINATE CONFUSION. I SHOULD HAVE ALSO IMMEDIATELY ASSERTED MYSELF (GOOD COCKPIT RESOURCE MGMNT) THAT THE GS SHOULD BE USED EVEN THOUGH WE WERE VFR. SUPPLEMENTAL INFO FROM ACN 246131: SINCE WE WERE BELOW NORMAL IFR VECTORING ALT; APCH CTL CALLED US WITH A WARNING ABOUT THE TWRS AHEAD. WE MAINTAINED LEGAL VFR SEPARATION ALT AT ALL TIMES; BUT WE WOULD HAVE CAUSED LESS STRESS ON THE CTLR IF WE WOULD HAVE MAINTAINED 4000 FT MSL UNTIL ON FINAL AND COMPLETELY CLR OF ALL OBSTRUCTIONS.