48-18-02 SIKORSKY: Applies to Model S-51 Series Helicopters Serial Numbers SS-51- 01 Through SS-5157.
Compliance required at first main gearbox overhaul but in any event not later than the next 400 hours of operation.
To prevent cracks caused by stress concentration at the corners of the internal splines on the bevel drive gear (Sikorsky P/N S-535360), a 1/32-inch radius relief should be formed at the lower end of each spline. The procedure for accomplishing this modification is given in Sikorsky Aircraft Information Circular No. 40 and No. 40 Revision "A".