Accident Details
On June 13, 2018, at approximately 1059 Pacific daylight time, a Schweizer 269C helicopter, registration N557DC, was substantially damaged during a departure attempt at North Las Vegas Airport (VGT), Las Vegas, Nevada. The helicopter was being operated as a personal flight under Title 14 Code of Federal Regulations Part 91, with the pilot planning to fly to Perkins Field Airport (U08) in Overton, Nevada. The pilot sustained minor injuries.
Pilot Account
According to the pilot, after starting the engine and performing startup and preflight checks, he increased the engine and rotor rpm. The helicopter had not yet become light on the skids. With the engine and rotor rpm at the "very bottom of [the] green range," the helicopter began to vibrate while still on the ground. The vibrations initially seemed normal but then worsened. The pilot stated that the helicopter was not yet at the point where he would proceed to hover, which would have included getting the helicopter light on the skids, lifting gradually, and having the engine/rotor rpm at the top half of the range. In response to what he identified as ground resonance, he lowered the collective and rolled off the throttle to abort the takeoff. The vibrations increased in severity and lasted about 20 seconds. The main rotor and engine then stopped, and the helicopter had rotated about 45° to the left.
Witness Observation
A nearby witness reported that the helicopter was shaking, with the main rotor blades "flopping up and down." The witness stated that the helicopter never came to full power or left the ground and that it "destroyed itself."
Postaccident Examination
Postaccident examination revealed substantial damage to the fuselage. Examination of the airframe showed no anomalies or evidence of preimpact mechanical failure that would have precluded normal operation. Flight control continuity was established to the main rotor and tail rotor blades. All landing gear dampers were examined and tested within the specified pressure/charge range, and no anomalies were observed on the skid attachments. Two main rotor dampers were separated from the main rotor blades and remained attached to the mast; visual examination revealed no anomalies. The attached main rotor damper was removed from the main rotor blade and was examined and tested with no anomalies noted. All main rotor blade dampers had been tested about 7 flight hours before the accident and met the specified criteria. Compliance was documented with a special airworthiness information bulletin on landing gear damper inspections (SAIB SW-17-29).
Pilot's Comments on Ground Resonance Guidance
The pilot stated that there are no procedures in the pilot’s operating handbook for the helicopter make and model for dealing with ground resonance on startup and that his training focused on ground resonance during the transition from flight to hover and as a result of skid-to-ground hard contact. The pilot further stated that the FAA guidance in the Helicopter Flying Handbook was focused on ground resonance occurring on skid-to-ground hard contact when the helicopter was already in the air. He also cited the guidance in the handbook regarding corrective action when rpm was low: lowering the collective and closing the throttle. The pilot stated that he had not anticipated that ground resonance could develop so easily without lifting the helicopter.
The Federal Aviation Administration’s Helicopter Flying Handbook (FAA-H-8083-21A), Chapter 11, Helicopter Emergencies and Hazards, included the following guidance on ground resonance: "If the rpm is low, the only corrective action to stop ground resonance is to close the throttle immediately and fully lower the collective to place the blades in low pitch. If the rpm is in the normal operating range, fly the helicopter off the ground." This guidance was listed after discussion of hard contact with the ground and when one other landing gear strikes the surface.