59-05-05 HILLER: Applies As Follows: (a) UH-12, UH-12A, and UH-12B Incorporating Hiller Service Bulletin Numbers 50 or 50A After July 1, 1957. (b) UH-12C, Serial Numbers 934 and Up. (c) UH-12D, All Serial Numbers. (d) All Spare P/N 34141 Castings Delivered By Hiller After July 1, 1957. All UH-12 Series and All Serial Numbers Incorporating These Spares Are Affected.
Compliance required as indicated.
Due to improper casting techniques, two cyclic control scissor castings, P/N 34141, have failed in service on Model H-23D helicopters. As there is a possibility that additional P/N 34141 castings are defective, the following measure are required to detect cracks and prevent further failures:
(1) Prior to every flight and refueling, visually inspect P/N 34141 casting for cracks if part has accumulated more than 275 hours. If cracks are detected, the part must be removed from service prior to further flight.
(2) Effective September 1, 1959, P/N 34141 casting (including basic number and all dash numbers) must be removed from service prior to accumulation of 275 hours total time.
(3) Upon replacement with a new forging P/N 34158, the special inspection of item (1) may be discontinued. This forging has unlimited service life.