Metaline Falls, WA, USA
N559D
Kaman HH-43F
The pilot was about to release a load of logs onto a log pile from an altitude between 150 to 200 feet when ground crewmen heard an explosion, then observed the helicopter descend in a nose down attitude before impacting the log deck. An examination of the accident site by an FAA inspector revealed that all major portions of the helicopter were accounted for. A subsequent examination of the wreckage revealed a failure of the transmission's left-hand cross-shaft internal spline, which resulted in the loss of gearbox timing and subsequent in-flight blade contact and separation. Maintenance records revealed that the helicopter's transmission was overhauled on May 1, 2006; the time between the overhaul and the accident was 409.4 hours. An examination of the fractured transmission center housing was caused by two fatigue cracks, which were probably caused by severe cyclic stresses that resulted from repeated loading and unloading of logs.
HISTORY OF FLIGHT On August 18, 2006, approximately 1600 Pacific daylight time, a Kaman HH-43F helicopter, N559D, was destroyed following a loss of control and impact with a log pile about 5 nautical miles southeast of Metaline Falls, Idaho. The helicopter was registered to a private individual and operated by Horizon Helicopters of Laclede, Idaho. The commercial pilot, sole occupant of the aircraft, sustained fatal injuries. Visual meteorological conditions prevailed for the logging operation, which was conducted in accordance with 14 CFR Part 133, and a flight plan was not filed. The flight departed from the accident/staging site approximately 1530. A ground crewman who witnessed the accident and was working at the accident site reported that the pilot was in the process of dropping logs on a log pile from an altitude of between 150 feet to 200 feet above the ground when he heard an explosion. The ground crewman further reported that he "...observed fragments of blades going everywhere. [I] turned to the helicopter [and] it was coming down nose first before impacting the log deck." A second witness to the accident reported hearing a loud noise and "...observing the top blown off and debris go everywhere before seeing the helicopter drop." On August 19, 2006, the wreckage was recovered from the accident site and transported to the operator's facility in Laclede, Idaho, where a detailed examination would be conducted at a later date. PERSONNEL INFORMATION A review of the Federal Aviation Administration (FAA) Airman and Medical Records databases disclosed that the pilot held a commercial pilot certificate with ratings for rotorcraft-helicopter and instrument helicopter. The pilot also held an instructor rating in helicopters. A second-class medical certificate was issued to the pilot on December 9, 2005, without limitations. On his most recent application for an aviation medical certificate the pilot reported a total time of 2,000 hours, with 500 hours flown in the past 6 months. Company records indicated that the pilot had accumulated the following flight hours in make and model: 897 total flight hours, 400 hours in the previous 90 days, and 7.2 hours in the last 24 hours. AIRCRAFT INFORMATION Horizon Helicopters holds the Type Certificate number "H1NW" for N559D, serial number 62-4514, a Kaman HH-43F series rotorcraft. (Refer to Attachment TC-I). The helicopter was acquired by the United States military and subsequently certificated by the Federal Aviation Administration for restricted category operations. N559D was powered by a Honeywell Aerospace T53-L-13B turboshaft engine, serial number LE-23398B, rated at 1,400 shaft horsepower. The operator reported that the helicopter was maintained in accordance with the FAA's Continuous Airworthiness Inspection Program with its most recent phase inspection having been completed on July 20, 2006, at a total airframe time of 7,960.3, and an engine total time of 4,263.5 hours; the total airframe time at the time of the accident was reported as 8,028.6 hours. Maintenance records further revealed that the engine was overhauled on July 2, 2004, at a total time of 2,910 hours, and that its last hot section inspection occurred on April 18, 2006, at an engine total time of 3,922.6 hours; 1,012.6 hours since being overhauled. Records also revealed that the helicopter's transmission assembly, part number K774502-3, serial number B18-7, was overhauled on May 1, 2006, at a component total time of 3,666.7 hours, a bearing total time of 646.0 hours, and a total airframe time of 7,619.2 hours. At the time of the accident the transmission had accumulated 409.1 hours since overhaul. (Refer to the attached Kaman HH-43 Component Historical Record - Transmission Assembly, and the Main Transmission Overhaul Data sheet.) WRECKAGE AND IMPACT INFORMATION An on scene examination of the wreckage by an FAA airworthiness inspector revealed that the helicopter came to rest on its left side facing in an east-southeast direction in a forested clearing used as its operational base for logging operations. The inspector reported the physical location of the accident site was at coordinates 48 degrees 49.515 minutes north latitude and 117 degrees 17.785 minutes west longitude, at an elevation of 2,602 feet mean sea level. The accident site was approximately 4.3 nautical miles southeast of Metaline Falls, with the main wreckage located about 130 feet west of the west shoreline of Sullivan Lake. The inspector reported that his on scene examination indicated that all major portions of the helicopter had been accounted for. With respect to the wreckage distribution, the inspector revealed that the left-hand transmission tower was found 63 feet west of the main wreckage, while the right hand transmission was located 57 feet southwest of the main wreckage site. The helicopter's exhaust pipe was found 52 feet northwest of the main wreckage, the tail section located 20 feet northeast of the wreckage, while multiple pieces of the helicopter's main rotor blades came to rest in an area from northeast through southeast, approximately 80 to 100 yards from the main wreckage. MEDICAL AND PATHOLOGICAL INFORMATION On August 22, 2006, an autopsy was performed on the pilot by the Deputy Medical Examiner, Office of The Medical Examiner, Spokane, Washington. The cause of death was determined to be "blunt force impact of the head". Toxicology was performed by the FAA Civil Aeromedical Institute, Oklahoma City, Oklahoma. Test for carbon monoxide and cyanide were negative, while 24 (mg/dL, mg/hg) of Ethanol was detected in Urine. It was noted that "the ethanol found in this case is from sources other than ingestion." No drugs were detected in the Blood. TESTS AND RESEARCH On September 6, 2006, at the request of the NTSB IIC, an airworthiness inspector from the FAA Flight Standards District Office, Spokane, Washington, accompanied by the Rotorcraft Program Manager assigned to the Seattle Aircraft Certification Office, Seattle, Washington, provided oversight during an inspection of the helicopter conducted by personnel from Honeywell Aerospace, Phoenix, Arizona, and Kaman Aerospace Corporation, Bloomfield, Connecticut. The examination revealed a failure of the left-hand cross-shaft internal spline, which resulted in the loss of gearbox timing and subsequent in-flight blade contact and separation. The examination further revealed that the left and right transmission heads were separated. The female drive splines connecting the left and right aircraft transmission heads were stripped; the male drive shaft splines were intact. An examination of the aircraft's engine revealed that there was shredded wood debris located in the inlet housing, foreign object damage to the leading edge of the first-stage axial compressor blades, and metal spray deposits of the suction side of the vanes of the second-stage power turbine stator. The N2 rotating group was not free to rotate. (Refer to the attached Honeywell Aerospace report.) The fractured transmission center housing was shipped to the NTSB Materials Laboratory, Washington, D.C., by the IIC for examination. A Senior NTSB Metallurgist reported that a visual examination of the center housing revealed the fracture faces contained faceted features characteristic of a casting. Fracture lines emanated from the relief radius between the off-center post and circumferential wall on the lower right side of the off-center post. The exterior surface at the origin of the fatigue crack showed no evidence of mechanical damage. The fracture lines extended outward to a thumbnail feature consistent with the approximate terminus of a fatigue crack. The housing also exhibited a crack that intersected the relief radius between the circumferential wall and the off-center post on the upper right corner of the post. The exterior face of the wall in the general area of the fatigue crack showed no evidence of mechanical damage. The fracture faces that were located outside of the fatigue regions showed a river pattern typical of an overstress separation, with no evidence of crack arrest. (Refer to the attached NTSB Materials Laboratory Factual Report , #07-088) ADDITIONAL INFORMATION The aircraft, with the exception of the right hand transmission head housing and the left and right hand bevel gears, which were retained by the IIC, was returned to the registered owner on September 6, 2006.
The failure of the left-hand cross-shaft input internal spline while the helicopter was in a hover, which resulted in the loss of gear box timing, in-flight blade contact and separation, and the subsequent loss of control and impact with a log deck.
Source: NTSB Aviation Accident Database
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