Incident Overview
A pilot reported to the Federal Aviation Administration (FAA) that while spraying a cotton field and turning around from a swath run, the propeller feathered. In a separate statement to the National Transportation Safety Board (NTSB), the pilot said the aircraft "pitched upward and lost power."
Propeller Discrepancy
The aircraft type certificate specifies a Hamilton Standard propeller model number 2D30/6101A-12-13-14. However, the propeller removed from the aircraft was a Hartzell model HCB3W30-2B, which constitutes an unapproved installation.
Examination Findings
Disassembly of the Hartzell propeller revealed that a spacer had been placed in the ring assembly. This modification made it impossible for the propeller to feather. Additionally, the blade clamps inside the propeller hub were found broken. Examination of the blade positions showed that No. 1 blade was in the feathered position, No. 2 blade was near feather, and No. 3 blade was past feather.
Other Observations
Investigators found no evidence of oil loss or propeller governor failure or malfunction.