Minden, NV, USA
N447SH
Robinson R44 II
During a short-distance positioning flight, the helicopter descended uncontrolled into terrain about 5 minutes after departure. There was evidence that the main rotor diverged from its normal plane of rotation and severed the tailboom. Review of the pilot's personal flight logbooks showed that he had over 500 hours of flight time in helicopters. Visual meteorological conditions prevailed at the time of the accident with light winds and clear sky conditions. Examination of the wreckage showed that the fuel control return fuel line B-nut was not threaded to the fuel control fitting assembly and was melted. Metallurgical examination could not ascertain whether or not the B-nut was secured to the fuel control prior to the accident.
1.1 History of the Flight On February 7, 2006, at 0802 Pacific standard time, a Robinson R44 II helicopter, N447SH, collided with terrain and burned approximately 3 miles west of the Minden-Tahoe Airport, Minden, Nevada. The pilot was operating the helicopter under the provisions of 14 CFR Part 91. The helicopter was registered to DRACOR. The private pilot, the sole occupant, sustained fatal injuries. The helicopter was destroyed in the post-impact fire. Visual meteorological conditions prevailed, and no flight plan had been filed. The pilot departed from Minden about 0755. According to the assistant manager of the Minden airport, the helicopter was based at Minden. The pilot also owned two airplanes, and used the helicopter to commute between his home and the airport. The helicopter was always stored overnight in a hangar at the airport, unless it had been repositioned to the pilot's house. The Federal Aviation Administration (FAA) accident coordinator interviewed a friend of the pilot following the accident. The pilot's friend indicated that they had flown from Minden to the Madera, California area in the days leading up to the accident, and had returned to Minden the previous day. Due to poor weather conditions, they were unable to land at the pilot's home so they landed at Minden. The pilot was repositioning the helicopter to his home when the accident occurred. Repeated attempts by the National Transportation Safety Board investigator to contact the pilot's friend were unsuccessful. 1.1.1 Witness Information A witness was standing in her home and watched the helicopter come up over the trees and descend downward. The helicopter then made a sharp left turn and hovered for about 20 seconds. At that point, the witness stated that the helicopter began moving backward for about 1,000 feet. As the helicopter was moving backward, both the engine and helicopter sounds seemed normal to the witness. The witness thought that the helicopter was about 60 feet above ground level but due to her position from her residence, it was difficult for her to judge. As she watched the helicopter continue to move backward, the witness turned away from the window. Shortly thereafter, she heard the main rotor blades and engine become really loud and make a "clunking and rattle noise." She looked in the direction of where the helicopter had been flying, and noted a smoke plume. An additional witness reported that he was outside working when he heard what he thought was a single-engine airplane "over rev" its engine, "...as if in a hard turn or pull out of a dive." He looked up and saw a fireball erupt, followed by a muffled impact sound, and then a louder explosion. 1.2 Personnel Information The pilot held a private pilot certificate and was rated to fly single-engine airplanes under both visual and instrument flight rules. The pilot also held a rating for rotorcraft-helicopters. The pilot's last third-class medical was issued on January 28, 2004. There were no restrictions or waivers. The pilot reported a total flight time of 900 hours on the medical certificate application. On June 14, 2004, the pilot attended the Robinson Helicopter Company Flight Instructor Safety and Refresher Clinic. On his application he reported 500 hours in airplanes, 493 hours in helicopters. Of the helicopter hours, 467 hours were in a Robinson R22, and 25 hours were in a Robinson R44, with an additional 1 hour flown in an unknown make and model helicopter. Two personal pilot logbooks were obtained from the pilot's family. The first logbook ended in January 2003. The second logbook contained a combination of airplane and helicopter time. The last entry listed for airplane flight hours was dated March 8, 2004, and a total time of 497.9 hours was recorded in the single engine airplane section. The entry dated June 7, 2004, contained a note that any further single engine airplane information would be recorded in another logbook and helicopter time would be recorded in this logbook. The last dated entry in the logbook was December 4, 2004, and the pilot's total time in helicopters was recorded as 537 hours. 1.3 Aircraft Information 1.3.1 General Aircraft History FAA aircraft records showed that the helicopter was sold to DRACOR by Silver State Helicopters on May 18, 2004, and registered by the accident pilot on May 28, 2004. No maintenance logbooks were recovered for the helicopter. A maintenance record was obtained from Silver State Helicopters dated October 24, 2005, which indicated that Robinson Helicopter Company (RHC) Service Bulletin 55 had been complied with. The total time on the helicopter was 122.4 hours. The logbook entry noted that the fuel control unit was removed and retrofitted with KI-178 (the RHC fuel control reorientation kit). The fuel control was reoriented and reinstalled. All ground and operational checks were successful and no discrepancies were noted. 1.3.2 Fueling The most recent fueling record of the helicopter at Minden was dated February 2, with the addition of 31.5 gallons of fuel. A fueling receipt obtained from Madera Municipal Airport, Madera, California, showed that a helicopter with a registration number of "447NNN" was fueled with 13.1 gallons of 100 low lead on February 5. It could not be confirmed if this was the accident helicopter. 1.4 Meteorological Information The closest official aviation routine weather report (METAR) was reported at Lake Tahoe Airport, South Lake Tahoe, California. At 0753 the following conditions were reported: wind from 300 degrees magnetic at 6 knots; sky conditions, clear; temperature, 50 degrees Fahrenheit; dewpoint, 19 degrees Fahrenheit; and altimeter, 30.40 inches of Mercury. 1.5 Medical Information The Douglas County Sheriff's Department-Coroner completed an autopsy on the pilot. The FAA Forensic Toxicology lab completed toxicological testing. The results were negative for carbon monoxide, cyanide, volatiles, and all tested drugs. 1.6 Wreckage and Impact Information The FAA accident coordinator responded to the accident scene. The debris path covered an area of approximately 100 yards. The first identified wreckage consisted of main rotor blade pieces and a cut section of tail rotor drive shaft. Forward from this point approximately 40 yards, was the tail rotor assembly with a portion of the tail boom still attached. Between the tail rotor assembly and the main wreckage, a distance of 60 yards, tail boom debris was identified. The main wreckage sustained extensive fire and impact damage, coming to rest on its left side on a magnetic heading of 262 degrees; the left skid was crushed and the right skid remained intact. The main rotor blades remained attached at the main rotor hub. 1.7 Tests and Research The wreckage was examined on February 17, 2006, at Plain Parts located in Pleasant Grove, California. The NTSB investigator, a Robinson Helicopter Company (RHC) representative, a Textron Lycoming representative, and an airworthiness inspector from the Sacramento Flight Standards District Office, were present. The fuselage structure of the helicopter was consumed by fire. The seat structures had burned away. The tailboom separated approximately 4 feet forward of the tail rotor gearbox assembly. The tail rotor spun freely and produced corresponding movement to the fractured tail rotor drive shaft. The tail rotor pitch change push pull tube remained attached to the tail rotor and the pitch of the tail rotor blades changed when the tube was manually activated by hand. A 9 by 4 inch section of the outboard, leading edge of the horizontal fin was separated from the structure and located loose within the wreckage. The tailboom was twisted to the right just forward of the vertical fin. The tail rotor drive shaft had fractured into 5 sections. According to the RHC representative, three of the separations exhibited damage consistent with impact from the main rotor blades. The recovered portions of the tail rotor pitch change push pull tube had also fractured into 5 sections. The main rotor drive shaft was cut approximately 2.5 feet from the main rotor hub to facilitate recovery efforts. On main rotor blade serial number (SN) 0813B, the teeter stop was crushed and the metal surrounding the stop was bent. The leading edge was bent downward. Main rotor blade SN 0811B was bent upward and its teeter stop was melted. The majority of the blade excluding the leading edge had been torn or burned away from the remaining structure on both blades. The main rotor chip detector was removed and was free of contaminants. The skids sustained thermal damage on the left side and were fractured into several pieces. There was no evidence of rubbing on the underside of the skid tubes. The left skid was fractured from the remaining assembly. The helicopter was controlled through a series of control tubes and hydraulic servos. The forward sections of the control tubes were burned and not identified. From the lower portion of the fuselage, control tubes were traced to the mixing bellcrank located at the aft base of the fuselage structure. From this bellcrank, rod ends were present and the control tubes connecting the right, left, and aft hydraulic servos were identified. The Lycoming IO-540-AE1A5 engine, SN E-29326-48A, was rated at 2,718 rpm with 245 takeoff horsepower and 205 continuous horsepower. The top spark plugs from cylinders 1 through 5 were removed and the bottom spark plug from cylinder number 6 was removed. The coloration of the plugs varied and their gapping was similar. The cylinders were borescoped and no peening or gouging was evident on the cylinder walls. The entire accessory case was burned and the engine accessories were destroyed. The burned right magneto was secured to the case and the left magneto was hanging from its mounting point. The engine driven fuel pump was melted. Manual rotation of the engine was ascertained through the fan section and corresponding movement was noted to the accessory drive wheels. The oil pan was burned from the engine. The fuel control sustained fire damage. The throttle and mixture cables were attached at the arms, and the arms moved when actuated by hand. The low voltage-alt, oil pressure, engine fire, fuel filter, low rpm, main rotor chip detector, and tail rotor chip detector lights were sent to the NTSB Materials laboratory in Washington, D.C., for further examination. Examination of the filament for the main rotor chip detector caution light showed that the filament was elongated and distorted throughout its length, and according to the engineer, was consistent with having been illuminated upon impact. The low rpm and tail rotor chip detector lights were intact and not elongated or distorted. The remaining light filaments were destroyed by impact and fire damage. The fuel control return line and mating fitting assembly were submitted to the NTSB Materials laboratory for examination. The B-nut at the end of the fuel control return line was completely melted and resolidified around the steel end fitting of the line. The metallurgist stated that the return fuel line elbow fitting had contact markings both on the sealing cone and on the pressure flanks of the threads, indicating that a B-nut had been fully threaded onto it in the past. Soot and other debris partially covered the marks, which according to the metallurgist, indicated removal of the nut prior to or during the exposure to heat. 1.8 Additional Information On April 6, 2006, testing was performed at RHC in the same make/model helicopter, in which the fuel line between the fuel control and the fuel bypass pressure control valve was disconnected. A tee fitting was installed where the tee arm attached to a shut off valve, then to a length of tubing larger than the original fuel line. The end of the line fed into a fuel can. With the fuel shut-off valve CLOSED (a normal system), the helicopter was started, and the engine was warmed up per normal procedures. Power was increased to 22 inches of manifold pressure, and the shut-off valve was fully opened, with a steady fuel flow observed into the fuel can. The engine ran rough and seemed to surge. The low rpm warning light and horn came on and off with increases and decreases in rpm. The auxiliary fuel pump warning light illuminated steadily. With the shut-off valve opened, the helicopter was started per normal procedures. A steady stream of fuel flowed to the fuel can. No unusual symptoms were noted by the test pilot. The power setting was increased to 22 inches manifold pressure with no unusual symptoms noted. As the power setting was increased above 24 inches manifold pressure, the engine began to run rough and seemed to surge. The symptoms appeared the same as in the initial test. 1.8.1 Wreckage Release The wreckage was released to the owner's representative on February 7, 2007. No parts or pieces were retained by the NTSB.
The divergence of the main rotor from its normal plane of rotation for an undetermined reason, which resulted in main rotor/tail boom contact and loss of control.
Source: NTSB Aviation Accident Database
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