AD 53-24-02 ACTIVE

53-24-02 HILLER: Applies to All Model UH-12, UH-12A and UH-12B Helicopters.

Compliance required as indicated below.

There have been several recent failures of the tail rotor pitch change rod on UH-12B helicopters, resulting in loss of directional control. This pitch change rod, P/N 25036 or 25009, must be reinforced and/or inspected as follows on all UH-12 Series helicopters.

(1) Prior to the next flight and thereafter at periods not to exceed 10 hours operating time, remove the tail rotor pitch change arm and inspect the pitch change rod, P/N 25036 or 25009, in the shoulder area by dye penetrant method. If cracks are found the rod must be removed from service.

If no cracks are found, the pitch change rod is considered satisfactory for an additional 10 hours operating time. On reassembling the parts determine that chamfer of hole in arm does not interfere with radius on rod. If interference is noted, enlarge chamfer on arm to clear. Reinstall arm on pitch change rod, making sure woodruff key or bolt properly locates arm and that arm bottoms on shoulder. Install washer and nut on rod and torque to 50-75 inch-pounds (UH-12 and -12A Models) or 100-150 inch-pounds (UH-12B Models).

This periodic inspection must be continued until such time as the rod is reinforced as set forth in part (2).

(2) When the pitch change rod is reinforced by the addition of bracket, Hiller P/N 25104, the 10-hour inspections may be discontinued. Installation of this bracket is described in Hiller Service Bulletin No. 41. The service life of this installation is limited to 300 hours from time of modification.

This bracket, P/N 25104, should be installed as soon as possible but not later than January 31, 1954.