Amateur-built LONG EZ N754T accident near Eufaula, Alabama

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 analysis

The private pilot was conducting a personal flight in an experimental airplane. 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 ft short of the runway threshold in a rough, grassy area. 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 postaccident 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 inches long and between 1/8 and 1/4 inch 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.

Text from the NTSB. Open the NTSB docket for ANC18LA008 for the full record.