The pilot was conducting a personal flight in his experimental Long EZ.
While in cruise flight, the airplane “violently began shuddering,” and the pilot immediately shut down the engine and attempted an emergency landing. The airplane was unable to reach the selected runway and landed about 200′ short of the runway threshold in a rough, grassy area in Eufaula, Alabama.
After exiting the airplane, the pilot discovered that a portion of the trailing edge of the wood propeller had separated and penetrated the lower half of the right rudder control surface.
A post-accident examination of the remaining portion of the wood propeller determined that the propeller was manufactured from laminations of defect-free hard maple lumber that showed no signs of decay.
An inspection of the separation surface indicated that the individual layers of the propeller were laminated together using an adhesive that resulted in a light-colored bond line. The failure surface included an exposed portion of the bond line between two wood layers that had failed.
Examination of this bond line showed minimal wood failure that was about 8″ long and between 1/8″ and 1/4″ wide.
The amount of cured adhesive observed varied considerably along the length of the failure surface’s bond line, with an area of the bond line having minimal adhesive coverage.
According to the propeller manufacturer, the propeller was carved by hand and assembled using an adhesive that is advertised as “ideal for interior wood application.”
However, the adhesive had not been tested for applications in which extreme temperature fluctuations, pressure, and vibrations would be expected, such as those experienced during airplane operations.
Probable cause: The in-flight separation of a portion of the propeller, which subsequently penetrated the right rudder, as a result of the failure of the bond line between two of the propeller’s wood layers. Contributing to the failure of the propeller was the manufacturer’s use of an inappropriate bonding agent.
NTSB Identification: ANC18LA008
This November 2017 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.