AD 52-28-04

52-28-04 BELL: Applies to Models 47B, 47B3, 47D and 47D1 Helicopters (Prior to Serial Number 477).

Compliance required as soon as possible, but not later than January 10, 1953.

Magnetically inspect tail rotor pinion shaft, P/N 30-613-361, for damage and for cracks originating the keyway or fillet area. Replace shaft immediately if worn, damaged, cracked or if it does not pass the magnetic inspection satisfactorily. If the shaft passes the above inspections satisfactorily, or if a new shaft is being installed, accomplish the following prior to assembly: Place shaft in a lathe which is equipped with a grinding attachment. Use a 1/8-inch grinding wheel to increase the width of the recess at each side of bearing boss and grind a 0.030 to 0.040 inch radius at bottom of recesses. Reworked diameters of the shaft at the recesses at each side of the bearing boss are acceptable down to 0.763 inch and 0.604 inch respectively. These minimums must not be exceeded. Width of recesses are not to exceed 0.140 inch. There must not be any signs of the old radii or scratches.

(Bell Mandatory Service Bulletin No. 84, Revision B, dated April 29, 1953, covers the same subject.)