Shortly after the pilot applied full power and commenced the take-off roll there was a loud bang and the aircraft yawed violently. The pilot closed the throttle and stopped the aircraft. An inspection disclosed that one complete propeller blade was missing. A detailed inspection of the propeller blade indicated that the blade had failed in the area of the threads at the root of the blade. The fracture surfaces indicated that a fatigue crack had started approximately 500 hours prior to the final flight and that the blade had failed because the remaining unaffected metal could no longer carry the loads involved. The inspection was unable to find any reason for the origin of the fatigue crack. The cracking occurred in an area of the blade which is not visible when the blade is fitted to an aircraft, consequently the cracking could not be disclosed during either preflight or periodic maintenance inspections carried out in accordance with the maintenance system in force at the time of the failure. The blades are normally inspected for cracks at each overhaul. An overhaul is carried out after the blades have been in service for 1500 hours. The blade that failed had been in service for 1052 hours.
