59-19-02: Engine Cooling Fan Assembly

59-19-02 VERTOL: Applies to all Models 44A, B, and C Helicopters. Compliance required prior to next flight. Failures of the engine cooling fan discs, blades, and adapter rings have been experienced in Vertol 44 helicopters. The disc failures originated as a crack at the fan blade mounting hole on the forward face of the disc rim and then progressed to the point where a circumferential portion of the disc separated and penetrated the fuselage and helicopter buoyant float. The blade failures originated in the root radius on the convex camber and progressed through the blade section until the airfoil separated from the base. The adapter rings cracked through the holes to either the outer, inner, or both diameters. (a) To preclude recurrence of failures, the fan assembly, P/N 42P6410, must be retired and replaced with hub and fan assembly, P/N 42P6459-4. The new fan assembly includes a "Z" ring stiffener (P/N 04P9392-1) for the fan disc, thickened forged blades (P/N 42P6421-3) in place of the existing cast blades, and a steel adapter (P/N 04P6458-1) in place of the existing aluminum adapter, resulting in an infinite fatigue life of the assembly. (b) Fan disc assemblies, P/N 42P6422, which have been retried may be incorporated in the replacement 42P6410-8 fan assembly, provided no cracks are revealed by a Zyglo or dye- check inspection. Fan Disc assemblies having cracks must be destroyed or mutilated so as to preclude the possibility of their being returned to service. All cast blades P/N 42P6421-2 and aluminum adapter rings P/N 42P6458- 1, must be destroyed or mutilated to preclude their further use. (Vertol SDTM-1931 covers this same subject.)