49-47-02 BELL: Applies to All Models 47B, 47B3, 47D, and Model 47D1 Serial Numbers 145 Through 164.
Compliance as indicated.
As a result of recent failures occurring to the tail rotor drive system the following inspections and replacements must be accomplished:
1. Not later than the next 25 hours of operation and at each 50-hour period thereafter the following inspection procedure must be accomplished until the tail rotor drive shaft parts as described below are incorporated:
(a) Remove and disassemble tail boom extension for complete inspection.
(b) Visually inspect bearings for wear, cracks, chips, and brinelling.
(c) Inspect surfaces of shaft for dents, cuts, and signs of fatigue.
(d) Conduct a magnaflux inspection of the tail boom extension drive shaft, examining particularly the shaft surface for approximately 3 inches of length from each end of the shaft.
(e) Magnaflux 47-644-C14 sleeve inspecting for cracks at thread roots closestto flange.
2. To compensate for shaft misalignment and flight distortion of the shaft assembly, the following modifications shall be accomplished not later than February 15, 1950:
(a) Installation of a redesigned extension drive shaft P/N 47-644-126 and 47- 644-181.
(b) Installation of a spline coupling in tail rotor drive shaft forward of the universal joint P/N 47-644-177 and 47-644-130.
(Bell Service Bulletin No. 69, dated November 11, 1949, covers this subject.)