AD 58-20-04

58-20-04 VERTOL: Applies to All Models 42 Series and 44 Series Helicopters.

Compliance required as soon as possible but not later than December 1, 1958.

Fatigue failures of the 22D1073-4 jaw clutch driven and 22D1137-4 jaw clutch driver coupling have been found on both military and commercial Models 42 and 44 Series helicopters. Failure of the teeth of these couplings can preclude successful reengagement of the clutch, thereby disconnecting the rotor drive system from the engine. To prevent failures of this nature, both the aforementioned driver and driven couplings must be replaced by the new 42D1142-1 and 42D1143-1 driver and driven couplings respectively.

The replacement couplings are of a new twelve-tooth design and as such, require the replacement of the following additional parts and rework to account for differences in jaw teeth height and travel:

.... Parts to be replaced New replacement part Spring 22D1170-1 63D2363-1 Cam 3D3143 04D1043-1Ream two existing holes 0.3750/0.3755-inch diameter thru 42D1046-1 yoke and 42D1048-1 follower. Install 42D1008-2 pin and AN 381-3-10 cotter pin.

Drill and ream 0.3750/0.3755-inch diameter, two additional places, on 1.5 centerline thru 42D1046-1 yoke and 42D1048-1 follower. Install 42D1008-2 pins when yoke diameter is 1.00 inch. Install AN 381-3-10 cotter pins.

All couplings removed should be destroyed or permanently marked in a manner that will assure retirement from service.

(Vertol's S.D.T.M.-1866 covers this same subject.) This supersedes AD 58-10-04.