AD 75-07-08

75-07-08 SIKORSKY AIRCRAFT: Amendment 39-2138. Applies to Models S-58 and S-58T series helicopters certificted in all categories, including Military Type HSS-1, HSS-1F, HSS-1N, HUS-1, HUS-1A, HUS-1AN, HUS-1G, HUS-1Z, H-34A, H-34C, H-34J, CH-34A, CH- 34C, HH-34F, SH-34G, SH-34H, SH-34J, UH-34D, UH-34E, UH-34G, UH-34J, VH-34C, VH- 34D, equipped with S1610-31100 series rotary rudder assemblies and S1610-34200 series counterweight assembly.

Compliance required as indicated.

To prevent excessive stresses and possible structural failures in the tail rotor blades, tail rotor gear box assembly, and tail pylon area, from tail rotor unbalance, accomplish the following:

a. Within the next 10 hours time in service after the effective date of this AD unless already accomplished, lubricate and inspect the rotary assembly, P/N S1610-31100 series and counterweight assembly, P/N S1610-34200 series, for balance in accordance with Section 2, Paragraph A of Sikorsky Service Bulletin No. 58B15-14A, dated December 19, 1974, or later FAA approved revision.

b. Thereafter, lubricate and inspect at intervals not to exceed 50 hours time in service from the last inspection, or earlier if unbalance is suspected, in accordance with Section 2, Paragraph B of Sikorsky Service Bulletin No. 58B15-14A or later FAA approved revision.

c. If after two consecutive 50 hour repetitive inspections as specified in Paragraph b., the rotor balance remains unchanged, and within limits, these inspections can be extended to a 100 hour interval. These 100 hour intervals can be maintained if all subsequent 100 hour inspections show that rotor balance remains unchanged.

d. Rotary rudder assemblies, P/N S1610-31100 series and counterweight assembly P/N S1610-34200 series which are not balanced as specified in Paragraphs a., b., and c must be either rebalanced or removed for corrective action in accordance with Section 2, Paragraphs A and B of Sikorsky Service Bulletin No. 58B15-14A or laterFAA approved revision, before further flight.

e. The manufacturer's specifications and procedures identified and described in this directive are incorporated herein and made a part hereof pursuant to 5 U.S.C. 552(a)(1). All persons affected by this directive who have not already received these documents from the manufacturer may obtain copies upon request to Sikorsky Aircraft, Division of United Aircraft Corporation, Stratford, Connecticut 06602. These documents may also be examined at the Office of the Regional Counsel, New England Region, Federal Aviation Administration, 12 New England Executive Park, Burlington, Massachusetts 01803.

This amendment becomes effective April 8, 1975.