Cessna A185 N92DC accident near Aniak, Alaska

Probable cause

The pilot's inadequate preflight inspection, which failed to detect a crack in the propeller blade, which led to the separation of a section of a propeller blade due to fatigue.

NTSB analysis

The pilot/operator was taxiing the airplane for takeoff. While the airplane was moving about 15 mph and about 2,700 rpm, a blade from the metal two-blade propeller separated. After the separation, the pilot maintained control of the airplane and shut down the airplane. The engine mount sustained substantial damage from excessive vibrations caused by the propeller blade separation.

An examination of the fractured propeller blade revealed that it had failed due to fatigue cracking that had initiated from a nick in the leading edge. Measurement of the nick revealed it was within tolerance for a field repair although a field repair had not been performed.

The airplane was frequently used at unpaved runways and airstrips in remote locations. It is likely a nick was sustained on the propeller during the backcountry operations; however, it could not be determined when that nick occurred or when the fatigue crack was initiated.

The airplane manufacturer owner's manual indicates that the propeller should be checked for nicks during the preflight inspection. It is likely the pilot/operator did not adequately inspect the propeller during the preflight inspection. Had an adequate inspection been completed, the nick likely would have been identified and could have been field repaired.

Text from the NTSB. Open the NTSB docket for ANC17LA052 for the full record.