On October 9, 2001, at 1700 Hawaiian standard time, a Hughes 369D helicopter, N622WA, was involved in a passenger injury accident during takeoff from an industrial landing zone on Kahoolawe Island, Hawaii. The commercial pilot was not injured and one passenger was seriously injured. Two other passengers, who had previously deplaned and were walking away from the helicopter, were not injured. The helicopter was not damaged. The helicopter was being operated under 14 CFR Part 135 by Windward Aviation, Inc. Visual meteorological conditions prevailed and no flight plan was filed for the local area flight, which was shuttling workers between sites on the island. According to the operator, the accident occurred at the completion of a flight that repositioned the three workmen at a central location from which they would be further transferred to Maui. The helicopter landed with the intention of deplaning the three passengers with the engine operating and rotors turning. Two of the passengers deplaned and then gave the pilot a "thumbs up" to signify they were clear of the helicopter and he could takeoff. However, the third passenger realized he had left an item of property aboard the helicopter and attempted to retrieve it. The third passenger was reaching into the helicopter as the pilot lifted off for departure and the passenger fell to the ground. The injured passenger reported that when the helicopter arrived to pick them up, the pilot signaled by hand gesture that they could board. He approached the right, rear seat, and placed his lunch cooler and handheld radio on the floor in the center cabin. He noted that the bench seat was loose and not secured to the rear cabin bulkhead on his side of the aircraft. There were no doors installed. He fastened his seatbelt and was reaching for the headset to tell the pilot about the loose seat when the pilot abruptly took off. He described the ensuing flight as a "thrill ride" with abrupt climb, descent, and turns. He abandoned efforts to put on his headset and hung onto a safety strap with his right hand and the loose seat frame with his left hand. After landing, he pushed the loose seat back and unfastened his seatbelt and climbed down and stood along side the helicopter. He retrieved his cooler and radio and was refastening the seatbelt ends when he heard the engine power increase and watched the ground move away. He believed he only stood outside the helicopter 10 or 15 seconds before the liftoff. He believed that during the liftoff he was straddling the right-hand gear strut hanging with his head down and forward. He recalled that he considered climbing back into the helicopter and then his next recollection was of being on the ground, injured. According to the front seat passenger, one of the two who had deplaned and was not injured, prior to takeoff he had asked the pilot to ". . . give us a joy ride (hangtail in the air). . ." After landing, as he was getting out of the helicopter, he observed the third passenger, who was later injured, out of the helicopter and fastening his seatbelt halves together. The front passenger and the second passenger then walked away from the front of the helicopter talking about the "joy ride" they had. When the second passenger turned around to ask the third passenger a question, they noticed he was not walking with them and they then saw him lying on the ground. The front seat passenger said that reports from the pilot that they gave him a "thumbs up" are untrue. "Neither [the second passenger] nor I gave him the thumbs up." The second (uninjured) passenger told the Safety Board investigator he had been seated in the left rear seat. He did not give the pilot a "high sign" after deplaning. The pilot was completing his manifest as he and the front seat passenger walked away to the front of the helicopter. When they were 35 - 40 meters in front of the helicopter, he heard it power-up for takeoff and then, a short time later, power down. When they looked around they saw the third passenger laying on the ground. He recalled that the back seat was loose from the floor on the right end but that the seatbelt was attached to the floor, not the seat. There was no headset available for the left, rear passenger, and there were no real procedures in place for boarding and deplaning before the accident.