Los Angeles Airways Flight 417 - Findings

Findings

In the course of the investigation by the NTSB they made the following findings:

  1. The aircraft gross weight and center of gravity were within limits.
  2. The crewmembers were qualified for the flight.
  3. The yellow main rotor blade separated in flight rendering the aircraft uncontrollable.
  4. Blade separation was due to fatigue failure of the spindle.
  5. The fatigue crack was a high-cycle, low-stress type which propagated over a long period of time.
  6. The crack initiated because of a combination of the following factors:
    1. Metal hardness below specifications associated with a banded microstructure.
    2. Improper peening of the base metal surface.
    3. Possible detrimental effect of residual tensile stress from the plating.
    4. Pitting which may have been present in the base metal surface.
  7. It is believed that the crack was present at the last magnaglo inspection of the part, and it is not known why it was not detected.

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