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On February 21, 1997, about 0909 hours Hawaiian standard time, a Hughes HU-369-D, N505RM, operated by Manuiwa Airways, Inc., d.b.a. Volcano Hili-Tours, experienced the loss of its tail rotor assembly during cruise flight. The flight was operating under 14 CFR Part 135. The helicopter was substantially damaged during the pilot's forced landing on rough terrain about 5 miles southeast of Milolii, Hawaii. The commercial pilot and two passengers were seriously injured. The fourth passenger received minor injuries. Visual meteorological conditions prevailed, and a company VFR flight plan was filed. The local flight originated from a remote area approximately 1.4 miles north of the crash site about 0850.
The purpose of the flight was to transport personnel from the State of Hawaii's Department of Land and Natural Resources, Division of Forestry and Wildlife, to a work site within the Manuka Forest Reserve, in the South Kona District of the island of Hawaii. The personnel had been directed to spray fountain grass.
The passengers and their equipment boarded the helicopter, and the flight commenced. The pilot did not report that anything unusual occurred until after he leveled off at 90 knots airspeed and 400 feet mean sea level. The pilot indicated that about 1 minute after taking off he heard a loud bang, and immediately thereafter he felt a slight shudder in the tail rotor pedals. When he applied pressure to the tail rotor pedals there was no response. Seconds later the helicopter entered a steep left nose tuck attitude. The pilot reported that he regained control, flew for several minutes, and then began an autorotation. The helicopter touched down hard in an area covered with vegetation and rolled over. The engine continued operating and the main rotor blades continued rotating after the ground impact.
The left rear seated passenger reported that about 1 minute into the flight he heard a loud bang. Thereafter, he observed pieces of tail rotor blades flying past the left side of the helicopter.
The pilot passed an Federal Aviation Administration (FAA) proficiency flight check on November 25, 1996. The flight was performed in the accident helicopter, and was conducted by personnel from the FAA's Honolulu Flight Standards District Office. No training or airman proficiency deficiencies were reported.
On February 19, 1997, the operator's director of maintenance examined the helicopter and observed that one of the two tail rotor assembly pitch change links exhibited excessive wear in the rod end bearing. The maintenance director removed the link. He replaced it with a serviceable link from his inventory. The replacement link had previously accrued about 100 hours of in-service use. The maintenance director further reported that he test flew the helicopter and determined it operated normally. The helicopter was placed back in service the following day.
Prior to the accident flight all of the helicopter's doors had been removed.
WRECKAGE AND IMPACT INFORMATION
The crash site is located in the Kapua-Manuka Forest Reserve, southwest of the Mamalahoa Highway at the following GPS coordinates: 19 degrees 6.80 minutes north latitude, by 155 degrees 51.11 minutes west longitude. The flight originated at 19 degrees 7.80 minutes north latitude, by 155 degrees 50.31 minutes west longitude. Component part separation occurred within an estimated 7,300 feet northeast of the crash site. Multiple searches for the missing two tail rotor blades, pitch change links, and the gearbox output quill shaft were unproductive.
The main wreckage was examined following its recovery from the accident site. The integrity of the power train, main rotor blades, and the flight control system was established. No pertinent maintenance anomalies were noted, except that a tail rotor assembly pitch change link had a recent replacement history. There was no evidence of fire.
TESTS AND RESEARCH
The tail rotor pitch link, which the operator had removed from the helicopter 2 days before the accident and had retained in its inventory, was examined under the supervision of the National Transportation Safety Board. The operator reported to the Safety Board that the link had been removed because its bearings appeared virtually worn out. The examination was performed on March 19, 1997, by C & H Hydraulics and Engineering, Acme-Divac Industries Division, in Newport Beach, California. The link was found to have worn out. No manufacturing defects were observed.
An inventory was performed of the items reported to have been carried on board the helicopter during the accident flight. All reported items were accounted for. None of the occupants reported being aware of any item exiting the helicopter during the flight.
The helicopter's tail rotor drive shaft and the tail rotor gear box housing were shipped to McDonnell Douglas Helicopter Systems (MDHS) in Mesa, Arizona, where they were examined under the supervision of the Safety Board. No evidence of preimpact defects was noted. MDHS laboratory personnel reported that the fracture surfaces exhibited evidence of tensile (instantaneous) overload. No evidence of fatigue was observed.
MDHS opined that the most likely initiator for the housing fracture was a vibratory or out of balance load (of undetermined origin) created by the tail rotor assembly rotation and unbalanced centrifugal force.
According to MDHS, events which potentially could produce the requisite force to fail the housing could result from: (a) tail rotor blade or related component failure, or (b) an event external to the helicopter such as foreign object impact damage to the rotating blade assembly.
All recovered helicopter wreckage was released to the owner's assigned insurance adjuster on March 1, 1997.