Cessna 172S N353MV accident near Santa Monica, California

Probable cause

The separation of a section of a propeller blade due to fatigue cracking. Contributing to the accident was the operator’s failure to comply with the manufacturer’s maintenance and inspection instructions.

NTSB analysis

The flight instructor was conducting a local instructional flight with a pilot-receiving-instruction and one passenger on board. The flight instructor stated that, after completing a normal engine run-up and upon applying full throttle, he heard a loud "bang," followed by a violent vibration. He retarded the throttle back to idle, and the engine stopped producing power. After exiting the airplane, he found that a section of a propeller blade was missing.

Examination of the remainder of the propeller blade revealed that it had failed due to fatigue cracking that had initiated from a preexisting discontinuity (defect) in the blade material. Although the defect was probably related to the blade's initial forging, this could not be confirmed.

The propeller manufacturer had issued a service bulletin (SB) for the accident propeller model and serial number, which recommended additional inspection requirements for propellers installed in aircraft, such as the accident airplane, that are used in flight schools. The SB advised that the propeller should be inspected for cracks and surface discontinuities in the area that the failure occurred every 1,000 hours. A review of the maintenance records revealed that, at the time of the accident, the propeller was about 1,630 hours past the SB-recommended inspection interval.

The propeller owner/operator's information manual required that the entire propeller be checked for corrosion cracks and other damage at each 100-hour and annual inspection and that the propeller be overhauled every 2,000 hours. The maintenance records showed that the airplane's most recent 100-hour inspection occurred slightly more than a month before the blade separation; the surface corrosion should have been visible on the blades at that time; therefore, it is likely that the propeller was not inspected as part of this inspection. Further, at the time of the accident, the propeller was 630 hours past the 2,000-hour time between overhaul interval. If the operator had complied with the manufacturer's maintenance and inspection instructions, the fatigue cracking likely would have been detected before the propeller failure.

Text from the NTSB. Open the NTSB docket for WPR15LA025 for the full record.