The aircraft collided with mountainous terrain while executing an instrument missed approach. The recorded radar data showed that the aircraft was about 4 miles past the missed approach point when the turn was initiated. The VOR RWY 6 approach has a 620 ft MDA and the missed approach point is defined as 3.8 DME on the Scaggs Island VOR 050 radial. The radar data showed the aircraft crossed over the airport descending through 1,800 ft MSL. The lowest altitude achieved by the aircraft was 900 ft MSL, which occurred just before the aircraft initiated the missed approach turn. The DME unit in the aircraft can function in both an internal frequency mode and a remote mode. In the remote mode, the DME provides information from the NAV radios. In the internal mode, the unit gives information based on the frequency set in the unit's internal memory. Examination of the DME revealed that the unit was in the internal mode and selected to the Concord VOR, not the Scaggs Island VOR.