Hughes 269B N9422F accident near Hampton, Georgia

Probable cause

Ground resonance during landing for reasons that could not be determined based on the available information.

NTSB analysis

While hovering, the pilot attempted to set the helicopter down. During the transition from hover to landing, the pilot noticed a vibration in the helicopter. He decided to “pull more power” in an attempt to regain a hover condition. When power was applied, the helicopter began to shake violently. He then “rolled the power off and secured the landing.” The helicopter sustained substantial damage.

A postaccident examination of the helicopter revealed that the four oleo landing struts were sufficiently extended; however, damage to the helicopter precluded measurement of the struts in the properly loaded condition. No maintenance was performed on the struts and no annotations about their condition were recorded during the most recent annual inspection.

Although the pilot did not initially report any anomalies with the engine, he subsequently stated that the engine had “sputtered” during the hover and later reported that he had noticed a vibration and loss of power during the hover. He advised that he was a student helicopter pilot and was not completely familiar with the types of vibrations that were “normal” versus those that were not, and he had discussed this with his instructor on previous flights. The examination of the engine revealed no evidence of pre-accident mechanical malfunctions or failures that would have precluded normal operation.

The investigation was unable to determine if the ground resonance was caused by improper maintenance of the oleo landing gear struts, the pilot’s improper landing technique, or a combination of both.

Text from the NTSB. Open the NTSB docket for ERA19LA173 for the full record.