52-28-03 BELL: Applies to All 47 Series Helicopters With the 47-645-002 Gearbox Installed.
Compliance required as directed.
Replace the tail rotor gearbox shaft, P/N 47-645-077-1, when it has accumulated 900 hours of operation.
(Bell's Mandatory Service Bulletin No. 83, Revision A, dated October 2, 1952, covers this same subject.)