AD 51-20-03

51-20-03 HILLER: Applies to the following Aircraft: Model UH-12, Serial Numbers 105 to 135, Inclusive. (Incorporating the Collective Pitch Ballast System); Model UH-12A, Serial Numbers 136 to 176, Inclusive, and 178, 180 and 181.

Compliance required as noted below.

In order to preclude the possibility of protrusion of the bushings from the collective pitch ballast system bracket with resultant reduction of the pitch range of the main rotor blades and restricted controllability, the following should be accomplished:

(a) As soon as possible but not later than September 1, 1951, and at each 25-hour inspection period thereafter, visually inspect the collective pitch ballast system bracket P/N 31125-1 for protrusion of either upper or lower bushing P/N 31120-1. Particular inspection should follow each application of grease to the bracket.

(b) If the bushing(s) are found to be protruding, the assembly should be reworked by installing set screws in accordance with United Helicopters Mandatory Bulletin No. 19.

(c) Inspection of the bracket as specified in part (a) may be discontinued after the rework described in part (b) has been accomplished.

(Hiller Helicopters Mandatory Service Bulletin No. 19 covers this same subject.)