ZENITH STOL CH 750 N699TX incident near Paragould, Arkansas

Probable cause

The improper installation of the propeller flange, which resulted in an in-flight separation of the propeller assembly.

NTSB analysis

The pilot reported that, during the climb after takeoff, the engine "developed an immediate and heavy vibration." The intensity of the vibration increased, and the pilot was considering shutting the engine down when the vibration abruptly ceased. Looking out the windshield, he observed that the propeller had separated from the airplane. The pilot subsequently executed a forced landing to a field. Metallurgical examination determined that the propeller separation was initiated by a fatigue failure of two propeller flange-to-engine crankshaft flange attachment bolts. Further examination revealed that an incorrect thread lock compound was used on the propeller bolts, and the presence of a second compound suggested that the bolts were not properly cleaned before installation. In addition, washers used in the installation did not correspond with the washers specified by the manufacturer. Finally, extensive fretting damage to the propeller and crankshaft flanges in conjunction with the limited number of flight hours indicated that the attachment bolts were not torqued sufficiently at the time of installation. Available maintenance records did not include any entry noting that the propeller assembly had been removed since the initial installation.

Text from the NTSB. Open the NTSB docket for CEN13IA387 for the full record.