Pilot Debrief

Bell 206 near Marathon, TX — 2020-08-08

Final reportCEN20LA328
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Date
2020-08-08
Location
Marathon, TX, USA
Aircraft
Bell 206
Registration
N284S
Category
Helicopter
Highest injury
Fatal
Fatalities
3
Phase of flight
Maneuvering

Probable cause

The in-flight loss of helicopter control for reasons that could not be determined based on the available evidence.

NTSB narrative

During an aerial survey flight when the helicopter was about 800 ft above ground level, the pilot felt a slight vertical vibration through the collective and airframe. The vibration immediately intensified to a severe lateral vibration in the main rotor system, and the pilot could not control the helicopter. While maneuvering for an emergency landing, the helicopter lost lift and impacted terrain short of the intended landing area, and a postimpact fire ensued. The pilot stated that the engine was producing power at the time of the accident. No evidence indicated an in-flight structural breakup, and all damage to the airframe occurred during the ground impact sequence. A fatigue crack was found on the leading edge abrasion strip of one of the main rotor blades. Given the flat fracture features of the fatigue cracking, the fatigue crack was present before the accident flight. However, this fatigue cracking showed no evidence of propagation into the blade spar and, therefore, was likely not a factor in this accident. The main rotor blade damage was likely due to ground and tailboom impacts; the examined portions of the main rotor blades showed no evidence of an in-flight failure of the main rotor blades. In addition, no evidence showed any flight control disconnections, and further postaccident examination to determine if the flight control system had fractured could not be performed due to the extensive thermal damage. The helicopter’s hydraulic system was unable to be tested due to the damage resulting from the postcrash fire. Examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. The reason for the in-flight loss of control could not be determined based on the available evidence for this accident investigation. The helicopter was not equipped with, and was not required to be equipped with, crash resistant flight recorders. The lack of flight recorder data for this accident precluded further evaluation of the accident circumstances and pilot actions. This accident demonstrates the need for crash-resistant flight and image recorders aboard turbine-powered, nonexperimental, nonrestricted-category aircraft that are not currently required to be so equipped, as previously recommended by the National Transportation Safety Board.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Pilot could have conducted a precautionary landing after first vibration felt.

NTSB coding

Evidence available

  • Video
  • Photos
  • 9 docket documents
View NTSB final reportView NTSB docket

Docket documents9

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