56-20-03 BELL: Applies to All Models 47B, 47B3, 47D, 47D1, 47G, 47G2 and 47H1.
Compliance required as soon as possible but not later than October 20, 1956.
Failure of the tail rotor hub retention bolts P/N 47-641-052-1 has occurred in service. The probable cause of the bolt failures experienced to date has not been determined and this problem is currently being investigated. At the conclusion of this investigation Bell anticipates supplying a newly designed hub retention bolt as a replacement for the present bolts. In the interim it is mandatory that a service life of 300 hours be established for the subject bolt. At this time it is necessary to remove the two tail rotor retention bolts and replace them with new retention bolts of the same part number.
(Bell Mandatory Service Bulletin No. 112 dated August 8, 1956, covers this same subject.)