On May 18, 2001, at 0816 Hawaiian standard time, a Cessna 337C, N2479S (Mokulele 3), experienced a loss of engine power in both engines and ditched in the ocean off the coast of Paauilo, Hilo, Hawaii. Mokulele Flight Service, Inc., owned and operated the airplane under the provisions of 14 CFR Part 135 as an on-demand air taxi flight. The tour flight, Circle Island Flight, was a counter clockwise tour around the big island. The commercial pilot and five passengers were not injured. The airplane sank in deep water, 150 feet, and presumed to be destroyed. Visual meteorological conditions prevailed for the local area sightseeing flight, and a company visual flight rules (VFR) flight plan had been filed. The flight departed the Kona International Airport, Keahole (KOA), Kailua/Kona, Hawaii, at 0700. The flight was scheduled to terminate at KOA. According to Hilo Air Traffic Control (ATC) personnel, radar services were terminated with the accident airplane about 0806 after the airplane had transitioned through the Hilo terminal area. The pilot was instructed to squawk VFR and a frequency change was approved. The pilot switched to a UNICOM frequency. At 0814, a company pilot reported to Hilo ATC that he had heard a mayday call on the UNICOM frequency. He indicated that a company airplane had crashed into the water abeam Paauilo. In the pilot's written statement, he indicated that he conducted a preflight inspection of the airplane that included a weather check, weight and balance, and inspection of the airplane. Once everyone boarded the airplane, he conducted engine run-ups with all gages, including the fuel gages indicating normal. The flight departed on the main fuel tanks, and were kept in that position throughout the duration of the flight. Near Paauilo, both engines started to fluctuate with a gradual power reduction. The pilot started the emergency procedures, advanced the mixtures, propellers, and throttles. He expected that one of the engines would have a greater surge, but that was not the case. He reported that the front engine was "going in and out of power." He checked the fuel pressure gages and saw that both needles indicated zero. He turned on both fuel boost pumps and checked that the magnetos were on both. There was no response. He then made several unsuccessful attempts to get a "fuel flow response" by switching both sets of fuel selectors to "various settings." Once the pilot was unable to deduce the nature of the problem, he realized that they were losing altitude. He turned his attention to his passengers and briefed them again on the emergency procedure for an ocean ditching. He reached over and opened the emergency exit door, made a mayday call, and then landed straight ahead. He felt the safest place to land was the ocean due to the calm and smooth conditions. The pilot stated that the airplane bounced twice before the final impact. The front windscreen collapsed on the final impact and the cockpit started to fill with water. The pilot exited through the front of the airplane. When he surfaced he saw that two passengers were at the surface inflating their life vests. The pilot swam to the right front of the airplane where he saw a third passenger surface. He then dove to the door, which was submerged, to assist the last passenger who was still in the airplane. The airplane was starting to sink, and he was unable to reach the passenger. The pilot resurfaced, and then saw the last passenger surface. A tour helicopter circled the area and dropped life preservers. Personnel from county rescue services had everyone out of the water and to the nearest hospital 15 minutes after the accident. Federal Aviation Administration (FAA) inspectors interviewed the pilot and passengers. The pilot and passengers reported that both engines quit at the same time. The pilot told the FAA that he did not visually verify the fuel quantity; instead he utilized the fuel gages as a reference for fuel quantity. The pilot further reported that he believed there were several gallons of fuel in the auxiliary tanks. When the engines quit, he switched to the auxiliary tanks, with no change in the loss of engine power. The FAA inspectors also interviewed the owner, refueler, and director of maintenance of the company. The airplane was refueled the previous night with 44 gallons of fuel. When the refueler visually checked the fuel level, he stated that the fluid was just below the top, about 1 inch, which should have been 75 gallons. There were no unresolved mechanical anomalies with the airplane prior to the accident flight.