Pahrump, NV, USA
N510JM
Robinson R44
During an approach to landing near a race track, the pilot noticed that the clutch warning light became illuminated for about 7 seconds along with fluctuations in main rotor rpm for about 4 seconds. The pilot shortened his approach, and subsequently heard the low rotor rpm warning horn. He saw the low rotor rpm warning light, and immediately initiated an autorotation to the racetrack. Due to oncoming high speed vehicles on the track, the pilot extended his approach slightly beyond the track, and made a run-on landing to a level dirt area. The helicopter rolled over, and came to rest on its left side, resulting in substantial damage to the fuselage and the separation of the tail boom. Examination of the airframe, engine, clutch drive train components, and the associated warning systems revealed no anomalies that would have precluded normal operation.
On April 5, 2008, about 1547 Pacific daylight time, a Robinson R44 helicopter, N510JM, was substantially damaged during a precautionary landing near Pahrump, Nevada. The commercial pilot and his two passengers were not injured. The helicopter was registered to J Williams Enterprises Inc. of Anaheim, California, and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed and no flight plan was filed for the local personal flight that departed from a private helipad at the Spring Mountain Race Track about 1527. The pilot reported that after an uneventful flight around the immediate area of the race track, he maneuvered for initial approach to the cleared area near the paddock area about 400 feet above ground level (agl). As he started the initial descent, the pilot noticed the clutch warning light illuminated for about seven seconds along with fluctuations in rotor rpm for about four seconds. The pilot shortened his approach and selected a landing area about 100-yards closer to his position as a precaution. As the helicopter descended through 150 feet agl, he observed the low rotor RPM light illuminate and heard the low rotor RPM warning horn while noting the rotor RPM was "diminishing quickly." The pilot immediately performed an autorotation with the intention of landing on the race track directly in front of his position. As the helicopter descended through about 20 feet agl, the pilot maneuvered the helicopter slightly beyond the track due to oncoming high speed vehicles on the track. The pilot performed a run-on landing to a level dirt area adjacent to the race track. Subsequently, the helicopter rolled over and came to rest on its left side. Examination of the helicopter revealed that the fuselage sustained structural damage and the tail boom was separated. On May 21 and 22, 2008, the helicopter was examined by representatives from Robinson Helicopters and Textron Lycoming Engines at the facilities of Robinson Helicopters, Torrance, California under supervision of the NTSB investigator-in-charge. Examination of the airframe revealed that all four drive belts were intact and undamaged. The sprague clutch engaged and disengaged with no anomalies noted. The main rotor gearbox and tail rotor gear box rotated freely by hand. Control continuity was established from the cyclic and collective controls to the main rotor blade system. Continuity from the anti-torque pedals to the tail rotor system was established. The tail rotor drive shaft was separated into three pieces. The fuel system was intact and undamaged. The main, auxiliary, and interconnect fuel vent lines were free of debris. The governor control box was removed from the helicopter and installed on a test bench. The governor control box was tested and functioned within the manufacturers new and overhaul operational specifications with no anomalies noted. The belt tension actuator was intact and undamaged. The actuator was removed from the helicopter and installed on a test bench. When tested, the actuator unload (low limit) was measured at 1,452 pounds and the column spring load (high limit) was measured at 2,059 pounds. According to the manufacturer, the unload limit was within the acceptable range, however the column spring load (high limit) was 9 pounds over the specified limit of 2,050 pounds. According to the Robinson Helicopter representative, this condition would result in the belt tension system running for a fraction of a second longer. The engine remained attached via all its mounts. Throttle, mixture, carburetor heat control, and magneto continuity was established from the cockpit aft to the engine. The top spark plugs were removed and visually examined. When compared to the Champion Check-A-Plug comparison card, the top spark plugs exhibited normal operational signatures. Rotational continuity was established throughout the engine and valve train when the crankshaft was rotated by hand using the cooling fan assembly. Thumb compression was noted on all six cylinders. Magneto to engine timing was verified at 24 degrees and 25 degrees before top dead center. The airframe fuel sump drain was removed from the airframe and exhibited a small amount of dirt and lint material. The airframe fuel sump drain screen was not obstructed. The engine was started and ran for about two minutes on the airframe. White smoke expelled from the exhaust during the engine run and gradually subsided as the engine continued to run. A magneto check was performed with no anomalies noted and was found to be within manufacturer specifications. In order to facilitate the engine run on the airframe, the rotor brake system switch actuator was bypassed. The engine was removed from the airframe and installed on an engine test stand. The engine was started and run throughout its designated power range (idle to full power) for about eight minutes with no anomalies noted.
The loss of the engine to transmission drive train continuity while on approach for undetermined reasons. Contributing to the accident were lack of suitable terrain for a run-on landing, and cars on the race track.
Source: NTSB Aviation Accident Database
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