On April 10, 1994, about 1345 Atlantic standard time, a Bell 206B, N39125, registered to Hill Construction Corporation, crashed into the Caribbean Sea near Mayaguez, Puerto Rico, while on a 14 CFR Part 91 aerial observation flight. Visual meteorological conditions prevailed at the time and no flight plan was filed. The aircraft received substantial damage and the airline transport-rated pilot received minor injuries. One passenger received serious injuries, one passenger received minor injuries, and one passenger was not injured. The flight last departed Mayaguez, Puerto, Rico, on April 10, 1994, about 1315. The pilot stated he was flying from the right seat and the purpose of the flight was for photography of a boat race. They were flying in a left side slip at about 80 to 90 knots and 30 feet off the water. He did not remember any warning lights or horns activating. The aircraft started to yaw to the left and descend. The aircraft then hit the water and nosed over were it came to rest inverted in the water. He stated he did not remember all the events surrounding the accident. The passenger who was seated in the left front seat stated they were flying at about 35 feet heading north at 90 to 100 knots. He heard the engine spool down and heard the pilot state that they had lost the engine. The aircraft descended and the pilot pulled the nose up. The tail hit the water and then the main rotor blades began to contact the water. The aircraft then cartwheeled and came to rest inverted in the water. FAA inspectors examined the aircraft after recovery from the water. The aircraft structure and flight control linkages indicated no evidence of precrash failure or malfunction. The main rotor and tail boom were not recovered. Some contamination was found in the airframe fuel filter. Fuel was found in all fuel lines and engine components. The engine assembly was removed and shipped to Allison Engines for examination. The airframe boost pumps and fuel lines were removed and shipped to Bell Helicopter for examination. Teardown examination of the engine indicated no evidence of failure or malfunction of the rotating assembly. The main fuel control and power turbine governor were removed and sent to Allied Signal for examination. No contamination was found within the main fuel control unit and no evidence to indicate precrash failure or malfunction of the main fuel control or power turbine governor was found. See attached Allied Signal report. Examination of the airframe fuel boost pumps and lines indicated no evidence of failure or malfunction. The contamination found in the airframe fuel filter was analyzed and compared to material from the airframe boost pumps and fuel lines. The contamination did not match any of the materials in the airframe fuel system and it was not identified. See attached Bell Helicopter report.