A fracture mechanics analysis was conducted to establish the fracture toughness of a controllable pitch propeller crank ring material required to prevent a fracture mode in which loss of a propeller blade occurs. Loss of the propeller was assumed to be prevented if fracture instability could not occur before the fatigue crack grew to a size beyond which crack growth would proceed radially through the flange of the crank ring and not around the circumference. The fracture analysis was conducted by modeling the cracked crank ring as a plate with a part-through crack in bending. Numerical solutions for part-through cracks in bending were combined with results for large crack length-to-plate width geometries for through cracks in bending to determine KI for the large crack size of interest. Values of KI with plastically adjusted crack lengths were converted to values of JI and crack driving force curves were generated. Estimates of the plastic collapse moment for the crank ring were made as an alternative method of determining fracture conditions. The results of the analysis are a minimum acceptable value of yield strength and curves of yield strength versus minimum acceptable values of JIR and Tmat at a crack extension of 1.27 mm as determined by a J-R curve test.