On November 23, 2001, at 1409 local ship time, a MDHI 369HS helicopter, N4265D, rolled over on takeoff from a fishing vessel in international waters of the Pacific Ocean near Rabul, Papua New Guinea. The helicopter was operated by Hoffman Helicopters, Inc., of Tamuning, Guam, for fish spotting operations from a tuna fishing vessel under 14 CFR Part 91 of the Federal Aviation Regulations. The helicopter was destroyed when it rolled off the ship's right side, sank, and was not recovered. The commercial pilot sustained minor injuries and the observer was not injured. Visual meteorological conditions prevailed for the local aerial observation flight, which was originating at the time of the accident. According to the operator's written report of the event, the helicopter rolled off the right side of the fishing vessel as the pilot began to liftoff the helipad. The rotor blades hit the side of the ship and the helicopter entered the water inverted and sank. The operator stated that the probable cause was that the right side tiedowns and the APU cable were not removed by the shipboard helper prior to the pilot attempting to liftoff. The pilot reported to the operator that he believed he had checked the tiedowns before getting in the helicopter, but that it was also hard to see the right-hand side of the aircraft on the pad. The operator also noted that the shipboard helper is a Chinese national who does not speak English well and that communications may not have been good. In the operator's written accident report, he noted that a Allison T63-A-720 engine was installed in the helicopter. According to Allison, the T63-A-720 is an engine type produced for the military and has a close equivalency to a 250-C20C civilian engine. The Federal Aviation Administration Type Certificate Data Sheet for the 250 series Rolls Royce Allison engines notes that certain military engines are eligible for use under the Civil Type Certificate if the civilian model is stamped on the data plate next to the military model designation, and, certain modifications are made prior to civilian use. The engine sank with the airframe and no determination could be made regarding the status of the engine installed in the helicopter. Review of the MDHI 369 series Type Certificate Data Sheet disclosed that the model 369HS should be equipped with a Rolls Royce Allison 250-C18A or 250-C18C engine; however, an acceptable alternate engine is the Rolls Royce Allison 250-C20. Comparison of the data for the 250-C20C and 250-C20 engines revealed differences in horsepower output, gas producer rpm, and temperature limits, among others.