47-51-11 BELL: Applies to Model 47B Series Helicopters.
Service experience indicates that the transmission pinion gear bearing life can be extended to 100 hours of operation providing rework in accordance with Bell Service Bulletin No. 47C4 dated December 4, 1947, has been accomplished. New bearings P/N 47-820-358-1 must be installed in the upper spider assembly pinion gears and bearings P/N 47-620-357-1 must be installed in the lower stage spider assembly pinion gear at the 100-hour teardown inspection. (In order to assist in determining the service life of these bearings, it is recommended that removed bearings be tagged with any pertinent information and returned to Bell Aircraft Corp., Attention: Helicopter Division, Fort Worth, Texas.)
(Bell Service Bulletin 47C4 revised December 4, 1947, covers this same subject.)
This supersedes AD 47-41-09.