 It was the deadliest plane crash in the history of Papua New Guinea.The subsequent investigation found that the flight crew had inadvertently retarded the power levers below the lowest position allowable in flight (known as "flight idle"), causing both propellers to overspeed and leading to a complete loss of engine power.A 'beta lockout' mechanism that would have prevented the overspeed even in case of erroneous power lever setting was available but not installed on the accident aircraft.