WPR12MA034

The pilot's failure to maintain clearance from mountainous terrain while operating in marginal weather conditions, which resulted in the impact of the horizontal stabilizer and lower forward portion of the fenestron with ground and/or vegetation and led to the separation of the fenestron and the pilot's subsequent inability to maintain control. Contributing to the accident was the pilot's decision to operate into an area surrounded by rising terrain, low and possibly descending cloud bases, rain showers, and high wind.

***This report was modified on July 25, 2014. Please see the docket for this accident to view the original report.*** The helicopter impacted terrain during a sightseeing flight scheduled to fly from the island of Maui to the island of Molokai and return. Visual meteorological conditions prevailed at the departure airport; however, scattered rain showers and low clouds were forecast and reported along the helicopter's route of flight. When the accident occurred, the helicopter was flying over mountainous terrain and likely traversing down one of several ridges leading from Molokai's central peaks toward the lower terrain near the shoreline in marginal weather conditions. Several witnesses reported that the accident occurred between rain squalls, and one witness reported that it occurred during a heavy rain squall. All of the witnesses reported that heavy localized rain showers with strong gusting wind conditions existed around the time of the accident. Two witnesses reported that their attention was drawn to the helicopter when they heard a "whoop whooping" sound. One of these witnesses observed the helicopter descending from the ridgeline, and the other witness, who was closest to, and had the clearest view of, the accident helicopter, reported that the helicopter went "straight down" and impacted the ground. The debris field leading up to the main wreckage was about 1,330 feet long and consisted mostly of pieces from the fenestron, which is a shrouded tail rotor, indicating that the fenestron separated from the helicopter before the main wreckage impacted the ground. The remainder of the helicopter was accounted for at the main wreckage site except for the outboard portion of the right horizontal stabilizer, which was not identified in any of the recovered wreckage. A detailed examination of the wreckage indicated that the accident sequence of events likely began when the pilot failed to maintain sufficient terrain clearance, and the horizontal stabilizer and lower forward portion of the fenestron impacted vegetation and/or terrain. The upward and aft loading at the horizontal stabilizer, more pronounced on the right side, sheared the right attachment fittings, which allowed the right side of the stabilizer to travel aft. The combined loading from the horizontal stabilizer and the fenestron's impact with vegetation and/or terrain caused the stress in the forward flange of the junction frame to exceed its ultimate design strength. The forward flange of the junction frame fractured, which allowed the fenestron to separate from the tailboom. The torque input from the tail rotor drive shaft caused the separated fenestron to rotate counter-clockwise, which drove the lower portion of the fenestron into the main rotor disc, where it was impacted at least three times on the left side. After the fenestron separated from the tailboom, the helicopter lost yaw control, and its center of gravity shifted forward, which caused it to become uncontrollable and, subsequently, descend to the ground.

The pilot was not in radio contact with air traffic control, and no distress calls were heard by other pilots during the timeframe of the accident. Blue Hawaiian Helicopters is a 14 CFR Part 135 air carrier and holds on-demand operations specifications. The company headquarters is located at the Kahului Airport, Kahului, with additional bases located in Hilo, Waikoloa, Honolulu, and Lihue, Hawaii. The chief executive officer, president, director of operations, and director of maintenance all reside in Kahului. The chief pilot and director of safety reside in Honolulu. On April 17, 1987 (later revised on August 30, 1995), the FAA's Honolulu Flight Standards District Office issued Helicopter Consultants of Maui, Inc., dba Blue Hawaiian Helicopters of Kahului, air carrier certificate number HCMA601E, which permitted the operator to conduct on-demand air carrier operations in the United States. Pursuant to the certificate, the operator was authorized to carry passengers in Eurocopter AS350 and EC130 B4 series helicopters under day/night visual flight rules (VFR). Operations under instrument flight rules (IFR) were prohibited. An autopsy was performed on the pilot on November 14, 2011, by Pan Pacific Pathologists, Wailuku, Hawaii. The FAA's Civil Aerospace Medical Institute performed forensic toxicology on specimens from the pilot with negative results for drugs of abuse and alcohol. Engine The Turbomeca Arriel 2B1 turboshaft engine (serial no. 23067) was removed from the helicopter and shipped to Turbomeca's Grand Prairie, Texas, facility for disassembly and examination. The disassembly and examination revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. Additional information can be found in the engine examination report located in the public docket for this accident case file. Fenestron, Tail Boom, and Horizontal Stabilizer Pieces of the Fenestron, tail boom, and horizontal stabilizer were shipped to NTSB facilities in Ashburn, Virginia, and Washington, DC, for additional examination. The tail boom is a simple stiffened tubular (semi-monocoque) structure that is attached to the fuselage. A drawing of the aft end of the tail boom is shown in Figure A, which is located in the public docket for this accident case file. The fasteners and horizontal stabilizer have been omitted for clarity. The Fenestron is attached to the aft end of the tail boom by a junction frame (shown in green on the right side of Figure A) that is riveted to the aluminum tail boom structure and to the composite Fenestron structure. The junction frame has three flanges: the forward flange, aft flange and vertical flange. There is a ring frame installed forward of the horizontal stabilizer (shown in green on the left side of Figure A). There are four longerons (shown in purple in Figure A), two on each side, installed between the forward ring frame and the aft junction frame. The horizontal stabilizer is a single piece unit that is installed through the tail boom and attached to the tail boom by two vertical attachment bolts (shown in red in Figure A). The upper and lower horizontal stabilizer attach fittings (shown in orange in Figure A) are attached to the longerons on each side of the tail boom. A shim plate is installed on each stabilizer fitting with two countersunk screws (shown in blue in Figure A). The horizontal stabilizer attachment bolts pass through the shim plates and the horizontal stabilizer spar attaching the horizontal stabilizer to the tail boom. Forward of the ring frame, the tail boom is of typical skin/frame/stringer construction with six internal stringers spaced unevenly around the circumference between the ring frame and the battery door cutout. The helicopter's tail boom transmits the Fenestron and horizontal stabilizer loads and moments to the fuselage. The loads and moments generated by the Fenestron are transmitted into the tail boom through the aft junction frame. The loads and moments generated by the horizontal stabilizer are transmitted to the tail boom through the attachment hardware (bolts, shim plates, shim screws, and attach fittings) to the four longerons installed between the forward ring frame and the aft junction frame. The four longerons together act to distribute the various stresses from the Fenestron and horizontal stabilizer to the tail boom structure, forward of the ring frame. The examination of the Fenestron wreckage revealed that several areas exhibited angled cuts and/or deformation of the composite and aluminum structure, rotor blades, stators, and the tail rotor drive shaft. All of the fractures and damage were mapped on an exemplar helicopter using colored adhesive tape. This procedure revealed that there were three distinct cuts through the lower portion of the Fenestron. One cut was located just aft of the junction frame, one was located at the midpoint of the tail guard, and one was located near the aft edge of the duct. The location, spacing, and deformation of the cuts in the composite and aluminum structure, rotor blades, stators, and the tail rotor drive shaft were consistent with the main rotor blades striking the lower Fenestron three times on the left side (rotor blades rotate clockwise as viewed from above). The aft portion of the tail boom with attached remnants of the horizontal stabilizer was cut from the wreckage for further examination. The upper portion of the tail boom exhibited buckling damage to the structure just forward of the ring frame. The location was immediately forward of where the four longerons attach to the ring frame and extended clockwise from about 10 o'clock to about 2 o'clock as viewed looking forward. There was also buckling damage from about 2 o'clock to about 6 o'clock as viewed looking forward that corresponded to the location where the right horizontal stabilizer was displaced forward. The two horizontal stabilizer attach bolts were disassembled and removed, and the stabilizer was extracted from the tail boom; the upper steel spar straps remained fastened to the spar on both the left and right sides. On the left side, the spar and skin structure was deformed aft and exhibited moderate to heavy fire damage. On the right side, the spar was intact from the attach point out to the production end about 20 inches outboard of the attach point, and there was soil and wood debris embedded in the space between the spar and the spar strap on the aft side. The right side spar strap was buckled away from the spar; the outboard end of the right side spar was deformed aft and twisted leading edge down. The right side of the horizontal stabilizer leading edge structure remained attached to the spar from the attach point to about 15 inches outboard. It was deformed up and aft between about 6 inches and 11 inches outboard of the attach point and was crushed against the spar between about 11 inches and 15 inches outboard of the attach point. There were some small pieces of the upper and lower trailing edge skins attached to the inboard 14 inches of spar. The remaining trailing edge of the stabilizer on the right side exhibited buckling damage from the centerline outboard to the attach point. On the left side, the horizontal stabilizer attach fittings, attach bolt, shim, and shim screws were generally intact. On the right side, the screws in the upper and lower parts of the attach fitting were fractured in shear overstress. The direction of shear showed that the right side of the horizontal stabilizer had been moving aft when the screws fractured. The attach fitting had impressions consistent with multiple impacts from the right horizontal stabilizer attach bolt. Metallurgical Examination The circumferential fracture of the forward flange of the junction frame was examined in the NTSB Materials Laboratory. In general, the fracture surface showed relatively rough fracture features that were light gray in color. Multiple