56-27-02 HILLER: Applies to All UH-12, UH-12A and UH-12B Helicopters Including Spares.
Compliance required as soon as possible but not later than February 28, 1957.
Investigation has revealed that defective welds may exist at the clamp lugs on the four upper lord mount supports on P/N 63100-2 lower frame assembly (engine mount), or on mounts, P/N 63100-2M, modified in accordance with Hiller Service Bulletin No. 51. Failure of this weld has resulted in tilting of the rotor mast and loss of collective pitch control. The following one-time inspection is required on the above mounts to detect possible defective welds which must be reworked as indicated.
1. If the engine mount is cadmium plated, no inspection of the weld will be required, since these lower frame assemblies have been fabricated subsequent to the period of questionable weldments.
2. If the engine mount is not cadmium plated, remove the paint from all four lord mount supports in the area of the clamplugs and inspect for identification markings in or around the weld at the clamp lugs. If the weld is stamped with either a 7 or 8 or no stamp at all, it will be necessary to remove the mount from service until such time as the lugs can be removed and rewelded to CAM 18 standards.
(Hiller Service Information Letter No. 111 covers this subject.)