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6. Failure of the bevel gear stopped rotation of the fuel pump, oil pump, and propeller control unit.
7. The engine, without pressure lubrication, was rotated by the propeller until the high-speed pinion failed, decoupling the propeller from the engine.
8. Failure of the high-speed pinion so damaged the propeller oil transfer housing that subsequent attempts to feather were ineffective.
9. An emergency descent was executed at nearly maximum airspeed.
10. During this high-speed descent r. p. m. of the windmilling propeller increased until loads imposed exceeded the designed blade retention strength and the propeller failed.
Probable Cause
The Board determines that the probable cause of this accident was the inflight separation of the No. 4 propeller as a result of excessive loads induced by a descent at too high an airspeed while the propeller was windmilling decoupled from the engine and its r. p. m. was known to be uncontrolled.
BY THE CIVIL AERONAUTICS BOARD
/s/ JAMES R. DURFEE
/s/ CHAN GURNEY
/s/ HARMAR D. DENNY
/s/ G. JOSEPH MINETTI
