AD 74-15-06
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Sikorsky Aircraft Corporation | S-58A | Airworthiness Directives; Sikorsky Model S-58 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-58B | Airworthiness Directives; Sikorsky Model S-58 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-58BT | Airworthiness Directives; Sikorsky Model S-58 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-58C | Airworthiness Directives; Sikorsky Model S-58 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-58D | Airworthiness Directives; Sikorsky Model S-58 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-58DT | Airworthiness Directives; Sikorsky Model S-58 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-58E | Airworthiness Directives; Sikorsky Model S-58 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-58ET | Airworthiness Directives; Sikorsky Model S-58 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-58F | Airworthiness Directives; Sikorsky Model S-58 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-58FT | Airworthiness Directives; Sikorsky Model S-58 Series Helicopters |
Unsafe Condition
Failure of the magnesium input and/or intermediate housings of the tail rotor gearbox assembly, P/N S1635-64000 series, which could result from corrosion or fatigue cracking.
AI-generated summary from the source AD text. Verify against the official source before acting.
Required Actions
Inspect nuts attaching the tail rotor gearbox to the pylon fitting, inspect input and intermediate housings, retorque the nuts, conduct repetitive inspections every 10, 20, or 50 hours time in service based on installed components, remove and inspect the gearbox assembly within 25 hours, inspect nuts every 50 hours, replace cracked housings or pylon fittings, and remove magnesium housings by specified dates replacing with aluminum versions.
AI-generated summary from the source AD text. Verify against the official source before acting.
Compliance Time
Within the next three hours time in service after the effective date of this AD, or whenever unusual vibration in the tail rotor system is experienced; within the next 25 hours time in service after the effective date for the one-time inspection; remove magnesium housings prior to July 31, 1978 (turbine) or December 31, 1978 (piston).
AI-generated summary from the source AD text. Verify against the official source before acting.
Affected Aircraft
Sikorsky Model S-58 series helicopters equipped with magnesium input and/or intermediate housings of the tail rotor gearbox assembly.
AI-generated summary from the source AD text. Verify against the official source before acting.
Source: Official FAA Source ↗
Retrieved: Apr 8, 2026
Rights: U.S. Government Public Domain
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