AD 52-29-01

52-29-01 HILLER: Applies to All Models UH-12, -12A, -12B Helicopters.

Compliance required by February 1, 1953, and thereafter following any unusually hard landing, or following any maintenance work requiring loosening of the cardan joint assembly attachment to fuselage, or removal of the forward tail rotor drive tube or tail boom assembly.

Separation of the components of the forward tail rotor drive slip joint assembly, and eventual power loss to the tail rotor, may result from a severely hard landing, or from misalignment of the yoke, and cam followers of the "T" fitting following tail rotor drive system maintenance work of the nature described above. The condition may not be detected immediately, as it is possible to transmit torque to the tail rotor with the "T" fitting cam followers bearing on the outside of the yoke fingers. Failure of the "T" fitting under such conditions, however, will eventually result.

The following procedure, or equivalent, is necessary to permit inspection for proper alinement at the times specified by the compliance requirements above.

On the outboard surface of the fingers of the yoke, and adjacent to the slot, lightly scribe two marks; one at 0.72 inch and one at 0.78 inch aft of the closed end of the yoke slot. Then lightly scribe a mark through exact center of bearing cap on cam follower, at right angles to the yoke slot. With the helicopter at rest in a level attitude the line on the bearing cap of the cam follower must lie within the marks scribed on the yoke fingers. If correction is found necessary, refer to the Maintenance Manual, Section V, subsections 5-206-5-223. The following part numbers are given for reference:

UH-12B (Military HTE-2, H-23B) Yoke P/N 24539-1. "T" Assembly P/N 24564-3. Fwd. Slip Joint Assy. P/N 24565.

UH-12, -12A (Military HTE-1, H-23A): Yoke P/N 24523-1. "T" Fitting P/N 24526-1. Cam Followers P/N 24543-2. Fwd. Slip Joint Assy. P/N24500-9.

The following Military Publications cover this subject: Navy BuAer Dispatch 131746Z September 13, 1952. Air Force TO 01-255HB-31, September 19, 1952.

(Hiller Field Service Letter CD-2992 covers this procedure.)