Pilot Debrief

ROBINSON HELICOPTER CO R66 near Colusa, CA — 2021-08-01

Final reportWPR21FA300
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Date
2021-08-01
Location
Colusa, CA, USA
Aircraft
ROBINSON HELICOPTER CO R66
Registration
N7000J
Category
Helicopter
Highest injury
Fatal
Fatalities
4
Phase of flight
Maneuvering

Probable cause

The pilot’s abrupt flight control input that led to mast bumping and a subsequent in-flight breakup.

NTSB narrative

The pilot was conducting a personal flight during daytime visual flight rules conditions with three passengers aboard. A witness who was driving on a nearby highway observed the helicopter flying on an easterly heading about 50 to 100 ft above ground level. The witness stated that the helicopter was initially straight and level but had suddenly made a sharp left turn. The witness briefly lost sight of the helicopter due to trees; when he reestablished visual contact, he observed the helicopter descend and impact terrain. Postaccident examination of the helicopter revealed no evidence of any pre-existing mechanical malfunction that would have precluded normal operation. The forward left and right control tube attachment bolts at the nonrotating swashplate were not located at the accident site or within the recovered wreckage. The flight control bolts most likely separated during the accident sequence as a result of an overstress fracture. No evidence of preexisting loosening of the attachment nuts, such as substantial thread imprints in the lug bores, was observed. This damage was consistent with the blade grips contacting the mast, commonly referred to as mast bumping, which occurs due to excessive flapping motion of rotor blades (specifically, up-and-down motion of the blade tips). It is likely that, during the flight, the pilot made an abrupt flight control input that resulted in a main rotor blade contacting the tailboom and a subsequent in-flight breakup. The reason for the pilot’s abrupt control inputs could not be determined.

Analysis

Primary failure mode
Loss of control
First missed decision gate
Pilot could have avoided abrupt cyclic input to prevent loss of control.

NTSB coding

Evidence available

  • FDR / data
  • ADS-B / radar
  • Photos
  • 13 docket documents
View NTSB final reportView NTSB docket

Docket documents13

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