SCHWEIZER 269C near Las Vegas, NV — 2018-06-13

Probable cause

The pilot’s failure to take the appropriate corrective action for ground resonance, which resulted in a loss of helicopter control.

NTSB narrative

The pilot was preparing to depart in the helicopter on a local flight. He stated that he powered up the helicopter and that, with the engine/rotor rpm at the “very bottom of [the] green range” and the helicopter still on the ground, the helicopter began to vibrate. The vibrations worsened, and in response to the 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 shut down, and the helicopter had rotated about 45° to the left. A nearby witness stated that the helicopter was shaking and that it never came to full power or left the ground. Postaccident examination of the helicopter, including the landing gear dampers, skid attachments, and main rotor blade dampers, revealed no anomalies that would have precluded normal operation. Further, the main rotor dampers were tested about 7 flight hours before the accident flight with no anomalies noted. The Federal Aviation Administration’s (FAA) Helicopter Flying Handbook (FAA-H-8083-21A) stated the following about 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." However, this guidance for ground resonance corrective action was listed in the same paragraph after discussion of hard contact with the ground and when one other landing gear strikes the surface. Although the pilot noted that the engine/rotor rpm was at the very bottom of the green range, the rpm was still in the normal operating range; his decision to lower the collective instead of taking off led to increased (and/or continued) ground resonance vibrations and the subsequent substantial damage to the fuselage.

Analysis

Primary failure mode

Human factors

First missed decision gate

Pilot could have aborted the startup earlier to prevent ground resonance.

NTSB coding

• Ground resonance · Standing-engine(s) operating

Evidence available

• 6 docket documents

Docket documents6

• PILOT/OPERATOR AIRCRAFT ACCIDENT REPORT, NTSB FORM 6120.1form
• RELEASE OF AIRCRAFT WRECKAGE, NTSB FORM 6120.15form
• FAA HELICOPTER FLYING HANDBOOK EXCERPTSother
• LOGBOOK EXCERPTother
• RECORD OF EMAILother
• AIRFRAME EXAMINATION REPORTreport

Related mishaps

• SCHWEIZER 269C

  2016-07-16 · Calhoun, GA

• SCHWEIZER 269C-1

  2014-06-17 · Allentown, PA

• EUROCOPTER AS350B3 2B1

  2012-11-23 · Newfield, AZ

• HUGHES 269A

  2011-10-14 · Fort Worth, TX

• SCHWEIZER 269C

  2011-07-29 · Darlington, MD