Donnelly, ID, USA
N134WC
KAMAN AEROSPACE CORP K-1200
While lifting a heavy external load off the ground, the leading edges of two of the logging helicopter's counter-rotating main rotor blades collided with each other. The collision resulted in the destruction of a significant portion of both of those blades and the separation of one of the two main rotor pylons. Control of the helicopter was no longer possible, and it impacted the terrain in the inverted position. Detailed postaccident examinations of the helicopter’s components, tests, and witness interviews did not reveal evidence of any pre-existing anomalies or malfunctions or of any pilot action that would have led to the blades colliding. Although the helicopter was operating at an estimated 288 pounds above its maximum certified gross weight of 12,000 pounds, there is no evidence that this played a role in causing or contributing to the blade-to-blade contact. The event that initiated the accident sequence was not determined.
HISTORY OF FLIGHT On June 16, 2010, about 1440 mountain daylight time, a Kaman K-1200 helicopter, N134WC, impacted the terrain about five miles west of Donnelly, Idaho. The commercial pilot, who was the sole occupant, was killed in the accident sequence, and the helicopter, which was owned and operated by Woody Contracting Inc., sustained substantial damage. The 14 Code of Federal Regulations Part 133 long-line logging flight had been airborne for about an hour and 40 minutes. The flight was taking place in visual meteorological conditions. No flight plan had been filed. According to the four witnesses near the site, the helicopter, which was using a 200 foot long-line, had just lifted a large log off the ground when the accident sequence began. Two of the witnesses were looking directly at the helicopter as it lifted the log off the ground, and the other two looked immediately toward the helicopter after hearing a very loud noise that coincided with the beginning of the accident sequence. The pilot of the helicopter, who intended to take the log to a collection landing area about one-quarter mile away, had already attempted to lift the log off the ground once, but other logs interfered with the lift, so he set it back down. The pilot then asked the hooker to reset the choker nearer to the end of the log, which according to one of the witnesses would cause the log to hang more straight down during the lift. The hooker therefore reset the choker nearer to the butt end of the log, whereupon the pilot transmitted that, "That is more like it." Soon thereafter, the pilot again began to lift the log. According to the two witnesses that had a good view of the log itself, the accident sequence began just after the log was completely off the ground. The two witnesses who were looking directly at the helicopter perceived the accident sequence to have begun when they saw what appeared to be an outboard section of one of the rotor blades separate and fly through the air. This was followed a "split second" later by a very loud bang or pop. To the two witnesses who were not looking directly at the helicopter, the sequence began when they heard the very loud noise. Both of these individuals, one of whom was about one-quarter mile away, and the other (the hooker) who was within 50 feet of the helicopter, immediately turned to look directly at the helicopter. The first thing that both of these individuals saw was a piece (pieces according to the hooker) of the rotor blade flying through the air. Almost immediately after the separation of the rotor blade piece (pieces), other portions of the helicopter's blades and structure began to separate. The helicopter then went out of control, descended toward the terrain, ultimately coming to rest inverted. There was no fire. According to all four witnesses, there were no unusual engine or rotor sounds prior to the initiation of the accident sequence. They all stated that everything looked and appeared normal prior to the separation of the first rotor blade piece. Two of the witnesses made the point of saying that they had worked around helicopters for a long time, and felt that they would have recognized any abnormal change in engine or rotor sound. One witness made the point that he had heard unusual engine and rotor sounds from other helicopters over the years, but that this time everything sounded perfectly normal. Of the two witnesses who were looking directly at the helicopter, the one closest to the event was asked if it appeared that the pilot ascended faster than normal or tried to jerk the log off the ground. He responded that the pilot had not done either of those things, and that the lift looked like any other lift involving a single large log. The witnesses that were in position to judge how close the helicopter was to any trees were adamant that its rotor blades had not come in contact with a tree or any other obstacle. PERSONNEL INFORMATION The pilot, a 64 year old male, held a Commercial pilot certificate, with a helicopter rating and an airplane single engine land rating. His last FAA airman's medical, a class 2, was performed on 3/18/2001, and was issued without limitations or waivers. His total pilot time as of the date of the accident was estimated to be 27,600 hours, with 12,600 hours in the Kaman 1200. His last flight review was on December 8, 2008, in a Robinson R-22. AIRCRAFT INFORMATION The aircraft was a 1996 Kaman Aerospace K-1200 KMAX helicopter, serial number A94-0006, registered as N134WC, and powered by a Honeywell/Lycoming T53-17A1 engine, rated at 1,500 horsepower. The helicopter's last progressive inspection under its Approved Airworthiness Inspection Program (AAIP) was on June 15, 2010. At the time of the accident, the airframe had accumulated 24,053 hours. METEOROLOGICAL INFORMATION At the time of the accident, the helicopter pilot was working under a 12,000 foot overcast ceiling, in winds that varied from calm to variable at six knots. Visibility was more than ten miles. The temperature was about 45 degrees F. WRECKAGE AND IMPACT INFORMATION The helicopter lifted the log from the ground about the 6,300 foot level of the southeast facing down-slope of North Business Mountain, at about 44 degrees, 45.771 minutes north by 116 degrees, 11.138 minutes west. At the termination of the accident sequence, the airframe came to rest inverted over the top of the log it had lifted, about 410 feet southeast of the lift location, at an altitude of about 6,180 feet. The airframe wreckage included the main fuselage, the nose and cockpit area, the main and nose landing gear, the engine, transmission, and right rotor mast pylon, both left and right stabilizers, and the tail boom, including the vertical fin and rudder. Both horizontal stabilizers were fully attached, and both vertical stabilizers were fully attached to their respective horizontal stabilizers. Both horizontal stabilizers had rotated about 180 degrees so that the leading edge of both were facing aft, and the bottom tip of both vertical stabilizers were facing toward the top of the fuselage. The outboard two-thirds of the trailing edge of the right horizontal stabilizer was bent down to about 90 degrees, and trailing edge of the top half of the associated vertical stabilizer was bent outward to about 90 degrees. The top half of the right vertical stabilizer was bent inward toward the fuselage at about 45 degrees, but the bottom half was in its normal alignment. The left horizontal stabilizer was undamaged, and its associated vertical stabilizer was undamaged except for an area near the forward portion of the bottom tip where it had been crushed inward about 10 inches by impact with a limb of the log that was being lifted. The tail boom had twisted counter-clockwise (looking forward) just aft of the tail boom mounting points, and its structural skin had been almost entirely ripped apart at that location. All five tail boom mounting bolts were connected through their fittings, and the fittings themselves were undamaged. The remainder of the tail boom, aft of where it had twisted/torn, was undamaged, and the rudder was fully connected and free to pivot. There was no evidence of any flight control surface anomaly or malfunction. The belly hook was in the open position, and the bow shackle on the upper end of the long-line was released from the hook. The long-line itself was wrapped around the fuselage and left stabilizer, then strung up into some nearby birch trees, and then back down to the remote hook. The remote hook was connected to the choker, which was still attached to the log about three feet from its butt end. There were no marks or damage on the long-line that would have been consistent with it coming in contact with the rotor blades. The transmission was in its correct location, but the KAFlex coupling between the engine and transmission had sheared, with the associated adapter rings still being attached to the transmission and engine respectively. The forward engine mounts had separated from the helicopter's airframe structure, and the aft engine mounts had been torn from the engine diffuser housing. The right pylon was attached to the transmission, but was partially separated along the outboard edge of the transmission top cover and pylon base. The mast still protruded from the top of the pylon, and was imbedded in the dirt under the inverted fuselage. The rotor hub assembly had fractured releasing blades 94A and 94B. The majority of the structure of blades 94A and 94B was found southwest of the fuselage about 470 feet and 440 feet respectively. The most outboard six and one-half feet of blade 94B was located at a later date about two-tenths of a mile south of the fuselage. The left pylon, including the upper cover and the planet gears, had separated from the transmission where the pylon bolts to the transmission top cover, and was located about 190 feet east of the fuselage section. It had come to rest inverted (mast tip imbedded in the soil), with about 12.5 feet of blade 169B and 3.5 feet of blade 169A still attached. The damper tube black end was attached to blade 169B, and the fractured damper tube white rod end was attached to blade 169A. The U-crank was still attached to blade 169B, but the U-crank on blade 169A had broken off and was lying alongside the blade section, connected only by the idler assembly. The grips and teeter pins associated with both blades were intact. The majority of the remainder of blade 169A was located in an area about 250 feet west of the fuselage. The remainder of blade 169B was more widely scattered, with much of the blade not recovered, including any structure that could be positively identified as being outboard of station 260. The servo flap for blade 94A was attached to both of its mounting brackets, and both brackets remained securely attached to the blade afterbody. The leading edge/spar of the servo flap for blade 169A was attached to both of its mounting brackets, and both brackets were securely attached to the blade afterbody. The servo flap afterbody for blade 169A had separated along a straight span-wise line about one inch aft of its pivot point along its top skin, and about two inches aft of the pivot point along its lower skin. The servo flap afterbody itself was found lying near the tail of the helicopter. Most of the servo flap for blade 169B was found about 230 feet north of the fuselage. Its leading edge/spar, including the stainless steel protection strip, was all present, and it retained about two-thirds of the outboard portion of its afterbody. The inboard end of the leading edge/spar itself was attached to the inboard mounting bracket and pitch change linkage, but it had fractured about four inches outboard of the pivot bearing, and was retained only by the pivot rod. Its outboard pivot bearing had been pulled from the associated mounting bracket, and the mounting bracket itself was found securely attached to about an 18 inch section of blade afterbody. The servo flap for blade 94B was fragmented and recovered in pieces. Its inboard fitting was securely attached to the blade body, but the inboard end of the flap leading edge/spar had separated at the inboard pivot bearing, and was retained only by the pivot rod and the pitch change linkage. The leading edge/spar protection strip was all present, although deformed and bent forward along its outboard most eight inches. The leading edge/spar structure was present, except for about its most outboard four inches. The outboard hinge fitting was recovered, but it was completely detached from the servo flap pivot bearing. Its forward one-half was attached only to a piece of blade honeycomb structure barely wider than the fitting itself, and its forward most three inches was bent up and aft. The leading edge of the fitting and its forward attachment bolt and nut were damaged and deformed toward the trailing edge, in a manner consistent with impact from a blade rotating counter to it. After the on-scene investigation was completed, the wreckage was recovered to the facilities of SP Aircraft, in Boise, Idaho, where the NTSB Investigator-In-Charge (IIC), oversaw a layout inspection of the entire wreckage, including the engine. At the completion of that inspection, blades 94B and 169B, which had witness marks indicating that their leading edges had come in contact with each other, were shipped to the Kaman Aerospace Corporation, in Bloomfield, Connecticut. There they underwent a series of X-ray inspections, overseen by a representative from the Federal Aviation Administration (FAA) Manufacturing Inspection District Office at Windsor Locks, Connecticut (MIDO -41). The blades were subjected to the X-ray process in order to determine whether there were any preexisting anomalies within the interior of the blades, and to specifically detect any existing span-wise/chord-wise cracks or span-wise delamination in the laminated spruce spar. At the completion of the X-ray inspection, blades 94B and 169B were shipped to the NTSB's Materials Laboratory in Washington, D.C., for further examination and analysis. Upon completion of the Materials Laboratory examination process, blades 94B and 169B were returned to the facilities of SP Aircraft, where the investigative team performed another inspection of the major components of the helicopter's drive train, flight control system, and rotor blades. That examination was overseen and directed by an NTSB Materials Research Engineer. In addition, four panel-mounted instruments were removed from the wreckage and sent to the facilities of Howell Instruments, Inc., in Fort Worth, Texas, for inspection and attempted data retrieval. That activity was overseen by an NTSB Air Safety Investigator from the NTSB's South Central Region. The aforementioned series of inspections and examinations determined the following: 1. All fractures associated with the separation of the left pylon from the transmission were consistent with overstress, with no indication of preexisting fatigue cracking found. 2. Both the forward and aft left pylon supports failed in overstress, with no indication of preexisting fatigue cracking found. 3. The pylon-to-pylon shear tie failed in overstress on its left side and on the upper channel of its right side. Its right side lower channel cracked, but did not fully fracture. There was no evidence of preexisting fatigue cracks. 4. Turning input to the transmission freely turned the right main rotor shaft and the right azimuth assembly. 5. Both the azimuth assembly and the five planet gears at the bottom of the left pylon turned freely. 6. None of the components of the left side planetary gear system exhibited any visible damage to suggest misalignment, binding or excessive wear. 7. The left and right transmission chip detectors were free of any contamination or metallic particles. 8. All the pivots, bellcranks, rod ends, and bearings associated with the cyclic and collective controls and the horizontal stabilizer control systems were still connected, except where separated by overstress fractures. The aforementioned components all moved freely except where binding occurred due to impact damage. 9. All four main rotor blades fractured in multiple locations, with the servo flap push-pull tubes generally fracturing adjacent to the rod end at the inboard ends of the blades, where they were connected to the U-crank and idler assemblies. All the fractures in the servo flap push-pull tubes were consistent with overstress separation. Blades 94A and 94B separated from the mast assembly at, or just inboard of, the lead-lag pivot. Blades 169A and 169B separated from the blade root about two feet outboard of the end of the blade grip. 10. Both blade 169A and 94A had fractured in two similar locations (about station 50 to 60, and again about station 230 to 240), and neither blade showed evidence of coming in contact with another blade or airframe structure outboard of about station 65. The fractures at both locations on both of the blades were consistent with separation in overstress, and no evidence of a pre-crash anomaly was detected at any of the fractures. Inboard of Station 60, both blades displayed evidence of contact with one another. The bottom skin of
The collision of two counter-rotating main rotor blades for undetermined reasons, which resulted in a loss of control.
Source: NTSB Aviation Accident Database
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