KUKUIHAELE, HI, USA
N889AT
AEROSPATIALE AS350-D
DURING A SIGHTSEEING HELICOPTER TOUR FLIGHT AT 1200 FEET AGL, THE PILOT HEARD AND THEN NOTICED A DECREASE IN THE MAIN ROTOR RPM. THE PILOT BEGAN A PRECAUTIONARY LANDING TO A BOULDER-COVERED LEDGE ABOUT 50 FEET FROM THE SURF LINE. WHEN THE PILOT ADDED POWER FOR THE LANDING, THE ENGINE FAILED TO RESPOND AND THE MAIN ROTOR RPM HORN SOUNDED. AFTER TOUCHDOWN, THE MAIN ROTOR AND TAIL ROTOR BLADES STRUCK THE ROCKS AND THE HELICOPTER ROLLED ONTO ITS RIGHT SIDE. A SUBSEQUENT ENGINE EXAMINATION REVEALED A FATIGUE CRACK IN A STEEL 'T' FITTING THAT ATTACHED THE PNEUMATIC PG ACCUMULATOR TO THE POWER TURBINE GOVERNOR. THE CRACK WAS LOCATED IN THE CHANNEL OF THE FITTING WHERE THE ADJACENT NUT RETENTION WIRE IS WRAPPED. A METALLURGICAL EXAMINATION REVEALED NO OTHER CONDITIONS THAT MAY HAVE CONTRIBUTED TO THE INITIATION OF THE CRACK.
HISTORY OF FLIGHT On August 11, 1994, about 1215 hours Hawaii standard time, an Aerospatiale AS350-D, N889AT, crashed during a precautionary landing about 2 miles west of Kukuihaele, Hawaii. The helicopter was being operated as a visual flight rules (VFR) sightseeing flight under Title 14 CFR Part 135 when the accident occurred. The helicopter, operated by Hawaiian Heli-Jet Inc., Waikoloa, Hawaii, sustained substantial damage. The certificated commercial pilot and six passengers were not injured. Visual meteorological conditions prevailed. Company VFR flight-planning procedures for designated tour routes were utilized. The accident flight originated at the Hilo International Airport, Hilo, Hawaii, about 1145 hours. This was a sightseeing flight. The pilot reported that the tour flight departed the Waimea-Kohala airport, Kamuela, Hawaii, about 0935 hours and proceeded to the Volcanoes National Park area and then landed at Hilo for fuel. After departure from Hilo, the flight proceeded northwest along the north shore of Hawaii. After crossing the Waipio Valley, the pilot was flying about 900 to 1,200 feet above the shoreline when he heard and observed the main rotor rpm begin to decrease. The pilot decreased the collective control and began a steeper than normal approach for a precautionary landing. The landing area consisted of a small shelf of 8-inch- to 2-foot- diameter boulders that sloped downward to the shore. During the landing, the pilot added engine power by increasing the collective pitch control. The engine did not respond and the main rotor low rpm warning horn sounded. The helicopter touched down facing in a southeast direction, about 50 feet from the surf line. The helicopter then began to slide off of the rock ledge toward the water. The main rotor and tail rotor blades struck the rocks and the helicopter turned about 270 degrees and then rolled onto its right side. When the helicopter came to rest, the engine was not running. CREW INFORMATION The pilot holds a commercial pilot certificate with a rotorcraft helicopter rating. Additionally, the pilot holds private pilot privileges with an airplane single-engine land rating. The pilot also holds an aircraft mechanic certificate with airframe and powerplant ratings. The most recent second-class medical certificate was issued to the pilot on August 13, 1993 and contained no limitations. AIRCRAFT INFORMATION The helicopter had accumulated a total time in service of 7,394.5 flight hours. Examination of the maintenance records revealed that the most recent annual inspection was accomplished on January 1, 1994, 290.4 flight hours before the accident. In addition, a 100-hour inspection was completed on May 20, 1994, 97 hours before the accident. The engine had accrued a total time in service of 2,469.2 hours of operation. The maintenance records note that a 1,200-hour inspection was accomplished on June 3, 1994, 97 hours of operation before the accident. The power turbine governor had accrued 1,459.9 hours of operation since being overhauled. Fueling records at Hilo airport established that the aircraft was last fueled on August 11, 1994, with the addition of 65 gallons of Jet A aviation fuel. Examination of the maintenance and flight department records revealed no unresolved maintenance discrepancies against the aircraft prior to departure. METEOROLOGICAL INFORMATION The closest official weather observation station is Hilo, Hawaii, which is located 40 nautical miles northwest of the accident site. At 1252 hours, a surface observation was reporting in part: Sky condition and ceiling, 1,500 scattered clouds, 4,000 feet overcast; visibility, 15 miles; temperature, 83 degrees F; dew point, 75 degrees F; wind, 080 degrees at 7 knots; altimeter, 29.96 inHg. WRECKAGE AND IMPACT INFORMATION National Transportation Safety Board investigators examined the helicopter wreckage at the accident site on August 13, 1994. The aircraft was lying on its right side, parallel to the surf line. Ocean waves repeatedly washed over the wreckage. All of the helicopter's major components were found at the accident site. The forward portion of the right landing gear skid tube was separated at the forward, cross tube attach point. The vertical stabilizer separated from the tail boom just aft of the horizontal stabilizer and was lying in the surf. The separated portion of the tail boom exhibited slight diagonal torsional wrinkling and tearing. The right horizontal stabilizer was bent downward about 90 degrees at the inboard end. The tail rotor gear box was separated from its attach point and was hanging from the tail boom. The tail rotor blades separated at their inboard ends. The main rotor blades were fractured about midspan. The top door pin of the right side sub-door was broken out of its fuselage retaining hole and the door was crushed inward. The helicopter was not recovered until August 15, 1994, where it was examined at the operator's facility. The separated end of the tail rotor drive shaft exhibited rotational scoring on its outer circumference. The aft end of the tail rotor pitch control tube was bent slightly upward at the point of separation. Safety Board investigators were able to operate the flight controls by their respective control mechanisms to the point of separation. The airframe fuel filter had not been by-passed and fuel pressure was available from the fuel tank to the engine-driven fuel pump. The oil tank chip detector was free of metal. The airframe oil scavenge chip detector contained a small sliver of metal. The No. 2 and 3 bearing chip detectors were coated with a brown, sludge substance. The engine accessory gearbox chip detector exhibited two small metal slivers. The power turbine section of the engine could be handrotated. The compressor section could not be rotated by hand. The engine was removed, sprayed with a preservative compound, and shipped complete to the Textron Lycoming facility in Stratford, Connecticut. TESTS AND RESEARCH On August 24, 1994, an engine examination, supervised by a Safety Board investigator, was conducted at Textron Lycoming Turbine Engine Facility, Stratford, Connecticut. The parties noted in this report participated in the examination. The manufacturer reported that the engine was placed in an engine test cell and successfully started after the fuel manifold and ignitors were replaced and run at flight idle (50 percent ng). The engine would only accelerate to 62 percent ng followed by an uncommanded decrease to 45 percent ng. The power turbine governor was disconnected and the engine achieved 95 percent ng. The power turbine governor was replaced and the engine operated normally. The power turbine governor from the accident engine was then examined and a leaking "T" fitting was found which attached a pneumatic (Pg) accumulator to the governor. The leaking "T" fitting was replaced and the accident governor reinstalled on the engine. The engine again operated normally. The "T" fitting from the Pg port of the power turbine governor was examined by the Safety Board Materials Laboratory. The examination revealed the presence of a crack in the fitting under its adjacent nut in the bottom of the channel utilized for the nut retention wire. The crack striations and rachet marks were consistent with fatigue. Visual and electron-scanning microscope examinations revealed no other conditions that may have contributed to the initiation of the fatigue cracking. ADDITIONAL INFORMATION WRECKAGE RELEASE The Safety Board released the wreckage, located at the operator's facility, to the operator on August 16, 1994. The engine was retained by the Safety Board for examination until its release to the operator on September 30, 1994.
a fatigue crack in the 'T' fitting on the power turbine governor pneumatic accumulator. A factor was the rough, rock-covered landing area.
Source: NTSB Aviation Accident Database
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