Accident Overview
On August 11, 2014, at approximately 2000 mountain daylight time, a McDonnell Douglas Helicopter 500N (registration N18GH) sustained substantial damage after impacting terrain during takeoff from a private residence near Idaho Falls, Idaho. The helicopter was registered to Kabrit LLC of Salt Lake City, Utah, and operated by the pilot under 14 Code of Federal Regulations Part 91. The private pilot and two passengers were not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight.
Pilot Report
The pilot reported that during takeoff, he initiated a vertical climb to clear trees and a residential structure. When the helicopter reached about 90 feet above ground level, it banked left and immediately began rotating. Despite his control inputs, the pilot could not regain control and initiated an autorotation "to get the torque out of the rotor head." The helicopter impacted the ground and rolled onto its right side. The pilot shut down the engine after impact.
Examination Findings
An examination of the helicopter was conducted on September 25, 2014, at SP Aircraft in Boise, Idaho, with representatives from Boeing Helicopters and MD Helicopters under NTSB supervision. The airframe exhibited damage to sheet metal skin and composite fuselage components. The front canopy frame and windscreen were broken and separated. The upper pylon and NOTAR inlet were damaged, with crushed and fractured composite structures.
Flight control continuity was verified from the control sticks to the upper flight controls, including the collective, lateral and longitudinal links, mixers, scissors assembly, pitch change links, and swashplates, which were functional but sustained impact damage. The anti-torque control linkage was continuous from the left pedal to the NOTAR fan pitch control mechanism, with continuity from the cable separation point on the tailboom to the rotating cone assembly. The rotating cone and bearings appeared functional.
The NOTAR system sustained extensive damage, including tailboom separation, pedal damage, and fan shroud deformation. The fan transmission showed no visible damage and rotated by hand. The fan driveshaft and gearbox were undamaged, but fan blades contacted the deformed shroud and sustained foreign object damage.
The main rotor system sustained substantial impact damage. Hub components exhibited damage consistent with sudden stoppage from terrain impact. All main rotor blades were substantially damaged, with fractures, gouges, bent spars, wrinkling, and tip damage. Several blades contacted the fuselage, cockpit, and tailboom.
The main transmission showed no external impact damage. Chip detectors were clean. The transmission support structure was undamaged. The main rotor driveshaft had fractured about three inches above the splined fitting into the transmission, with a smeared fracture surface consistent with overload. The engine-to-transmission shaft and over-running clutch appeared functional.
Weight and Performance
Weight and balance calculations performed by the manufacturer indicated the helicopter was within limits. Performance calculations for the helicopter's weight and weather conditions at the time of the accident verified it was within published operational limits for an out-of-ground-effect hover.