Flight Departure
Before departing on a 30-minute night flight to an island destination, the pilot set his altimeter to the field elevation instead of the broadcast barometric pressure from the nearby Automated Surface Observation System (ASOS).
Communication with Air Traffic Control
During the climbout, the pilot contacted Air Traffic Control (ATC), which provided an altimeter barometric pressure setting and advised of radar contact passing 2,500 feet. At that point, the pilot set his altimeter to an indicated altitude of 2,500 feet, rather than using the correct barometric pressure setting.
Arrival and Descent
Upon arriving in the area of the destination airport, the pilot found it covered by a low-level fog layer. Without obtaining an updated altimeter setting from the ASOS on the neighboring island or from the Automatic Terminal Information Service (ATIS) on the nearby mainland, he descended over the water in an attempt to find a way to reach the airport underneath the fog.
Impact and Investigation
Just after leveling off at what his altimeter indicated as 500 feet, the aircraft impacted the water. Investigation ultimately determined that at no time during the flight did the pilot set the aircraft's altimeter in reference to an issued barometric pressure.