AD 81-23-04 ACTIVE

81-23-04 SIKORSKY AIRCRAFT: Amendment 39-4251. Applies to all model S-76A series helicopters certified in all categories equipped with 76351-09000-058 or prior dash number main gearbox assemblies.

For main gearboxes with 650 hours or more time in service since new or last overhaul on the effective date of this AD, compliance is required within the next 100 hours time in service unless already accomplished.

For main gearboxes with less than 650 hours time in service since new or last overhaul on the effective date of this AD, compliance is required within the next 100 hours time in service or before the accumulation of 650 hours time in service, whichever occurs later, unless already accomplished.

To prevent possible failure of the splines between the main gearbox input pinion bevel, P/N 76351-09019 series, and the helical gear, P/N 76351-09020 series, accomplish the following:

1. In accordance with paragraph F of Sikorsky Service Bulletin No. 76-66-14, dated October 23, 1981, remove and conduct a one-time inspection of the input pinion bevel housing assemblies on the number 1 and number 2 sides.

2. Remove from service and replace with a serviceable assembly all assemblies in which-the torque in the nut retaining the input pinion bevel stack-up is found to be less than 100 foot pounds.

3. If the nut torque is found to be 100 foot pounds or greater, accomplish the following in accordance with Sikorsky Service Bulletin No. 76-66-14:

a. Retorque nut to 500 foot pounds.
b. Conduct a .001 inch feeler gage clearance inspection.
c. Conduct a rotational drag inspection of the main Timken bearing.
d. If clearance and drag inspections are satisfactory, return assembly to service.
e. If clearance and/or drag inspection is unsatisfactory, remove assembly from service, and replace with a serviceable assembly.

This amendment becomes effective November 9, 1981.