48-12-05 BELL: Applies to Models 47B Series and 47D.
Compliance required at next 100-hour teardown inspection if less than 600 hours have been accumulated. (If over 600 hours have been accumulated, this change must be accomplished immediately.)
Replace the dural shear screws in the transmission spider assembly with steel shear screws (P/N 47-620-485-1).
(Bell Service Bulletin No. 47C66, revised February 10, 1948, also covers this same subject.)