Lake Central Airlines Flight 527 departed Chicago, IL for a flight to Detroit, MI with intermediate stops at Lafayette, IN, Cincinnati, OH, Columbus, IN and Toledo, OH. The aircraft arrived at Columbus at 19:35 and took off for Toledo 17 minutes later. About 20:05 the flight was cleared from its assigned cruising altitude of 10,000 feet to descend to 6,000 feet and report leaving 8,000 feet and 7,000 feet. Shortly after commencing the descent, all four prop blades on the no. 2 engines separated. The no. 2 prop blade penetrated the fuselage. While yawing to the right, the fuselage failed along the line of penetrations and the Convair crashed. When the torque cylinder failed, prop pressure oil was lost, causing the blades to move to low pitch at a rate too rapid for the prop pitch lock to operate effectively. The prop oversped, causing the blades to separate in overstress. PROBABLE CAUSE: “The failure of the right propeller due to the omission of the torque piston nitriding process during manufacture, and the failure of manufacturing quality control to detect the omission.”