AD 58-23-01

58-23-01 BELL: Applies to All 47B, B3, D, D1, G, G2 and H1 Helicopters.

Compliance required as indicated.

Service experience indicates numerous failures of the tail rotor pitch change control bearing, P/N R4AF4 and alternate P/N's SIRP and 7R4AXIC. Failures of this bearing have been partly attributed to the pitch change control shaft being bent.

To preclude the possibility of losing tail rotor control, a service life of 100 hours' time in service has been established for the tail rotor pitch change bearings P/N's R4AF4, 47-641-146-1, SIRP, and 7R4AXIC. All bearings with 90 or more hours' time in service shall be retired within the next 10 hours' time in service after the effective date of this amendment, except that tail rotor pitch change bearings with 190 or more hours' time in service as of the effective date of this amendment shall be retired prior to the accumulation of 200 hours' time in service.

The bearing service life of 100 hours is predicted by the maintenance of a concentric pitch change control shaft to within the allowable tolerances. To insure straightness of the pitch change control shaft, P/N 47-641-034 or P/N 47-641-045, a 600-hour inspection for runout is required. The shaft must be inspected at the next 600-hour inspection or not later than December 15, 1958, and every 600 hours thereafter.

Inspect shaft for allowable runout as follows:

1. Remove shaft from tail rotor gear box in accordance with Bell Service Manual.

2. Mount shaft at acme screw thread end in collet.

3. Measure concentricity of bearing shaft diameter. This diameter must be concentric within 0.060 TIR.

4. If diameters are not concentric within 0.060, shaft must be straightened within this tolerance.

(Manufacturers Urgent Action Maintenance and Overhaul Instructions, Nos. S58-41 thru S58-47, H58-10, H58-11 and H58-12, dated October 3, 1958, cover same subjects.)

Revised September 21, 1961.

Revised January 18, 1963.