NTSB Identification: SEA05LA121.
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Accident occurred Monday, June 20, 2005 in Fairview, MT
Probable Cause Approval Date: 12/20/2005
Aircraft: Cessna 188A, registration: N2133U
Injuries: 1 Minor.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

While en route at approximately 100 feet above the ground during an aerial application operation, one of the airplane's two propeller blades separated from the propeller hub. Subsequently, the remaining propeller blade and hub separated from the airplane, culminating with the pilot making a forced landing to an open field. Examination of the propeller assembly revealed that the propeller blade model was the correct blade for the propeller; however, the propeller model was not approved for the Cessna 188A with a TCM IO-520 engine. It was also revealed that the propeller should have been filled with red dyed oil for crack detection. A visual inspection of the aircraft revealed no evidence of red dyed oil on the surface of either propeller blade or the propeller hub. A further inspection of the separated propeller blade indicated that the failure occurred within the outboard blade retention threads.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

While in cruise flight a separation of a propeller blade as a result of a propeller hub crack. Factors contributing to the accident included the installation of an unapproved propeller, and the failure to properly service the propeller with red dyed oil for crack protection.

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