Curtiss C-46 NC92857 had been flown from Newark to San Juan, June 4, 1949. During the time that the aircraft was on the ground at San Juan, the flap follow-up cable was replaced, and both engines were checked. Since the right engine misfired during the check, 13 new spark plugs were installed. Shortly before midnight, June 6, 75 passengers, including five infants in arms and 14 children between the ages of two and 12, boarded the aircraft. Since there were only 65 seats in the cabin which necessitated seating some of the passengers double in one seat. Although the Weight and balance manifest for the flight indicated a total weight of 44,500 pounds, the aircraft actually weighed 48.709 pounds, which was 3,709 pounds in excess of the 45,000 pounds certificated aircraft weight. At approximately 00:10 the aircraft taxied to runway 27 where the pre-takeoff check was accomplished at which time engines and flight controls operated normally. Takeoff was accomplished at 00:21 after the San Juan Tower had transmitted an instrument clearance to the flight authorizing it to cruise at 8,500 feet to Miami. One minute after the aircraft left the ground and at an indicated air speed of approximately 115 miles per hour and at an indicated altitude of 250 feet, the right engine began to backfire severely and lose power. No attempt was made to feather the propeller of the right engine. An emergency was declared, and the tower cleared the flight to land on runway 09. But, since airspeed was low and altitude could not be maintained, the aircraft was flown straight ahead for a crash landing 200 yards off the shore at Punta Salinas. During a six minute period that the aircraft remained afloat the crew pushed two uninflated life rafts into the water and furnished several passengers with life preservers. Considerable confusion existed during the ditching operation since none of the passengers had received any instruction in the location or use of emergency equipment. Of the 81 occupants, only 23 passengers and five crew members survived. PROBABLE CAUSE: “The Board determines that the probable cause of this accident was the loss of power of the right engine before the aircraft attained the optimum single engine climb speed which, together with the overloaded condition of the aircraft, resulted in it losing altitude and settling into the sea.”