AD 86-25-05
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Sikorsky Aircraft Corporation | S-58A | Airworthiness Directives; SIKORSKY AIRCRAFT Model S-58A, B, C, D, E, F, G, H, J, BT, DT, ET, FT, HT, and JT, CH-34, HH-34, SH-34, UH- 34, and VH-34 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-58B | Airworthiness Directives; SIKORSKY AIRCRAFT Model S-58A, B, C, D, E, F, G, H, J, BT, DT, ET, FT, HT, and JT, CH-34, HH-34, SH-34, UH- 34, and VH-34 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-58BT | Airworthiness Directives; SIKORSKY AIRCRAFT Model S-58A, B, C, D, E, F, G, H, J, BT, DT, ET, FT, HT, and JT, CH-34, HH-34, SH-34, UH- 34, and VH-34 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-58C | Airworthiness Directives; SIKORSKY AIRCRAFT Model S-58A, B, C, D, E, F, G, H, J, BT, DT, ET, FT, HT, and JT, CH-34, HH-34, SH-34, UH- 34, and VH-34 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-58D | Airworthiness Directives; SIKORSKY AIRCRAFT Model S-58A, B, C, D, E, F, G, H, J, BT, DT, ET, FT, HT, and JT, CH-34, HH-34, SH-34, UH- 34, and VH-34 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-58DT | Airworthiness Directives; SIKORSKY AIRCRAFT Model S-58A, B, C, D, E, F, G, H, J, BT, DT, ET, FT, HT, and JT, CH-34, HH-34, SH-34, UH- 34, and VH-34 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-58E | Airworthiness Directives; SIKORSKY AIRCRAFT Model S-58A, B, C, D, E, F, G, H, J, BT, DT, ET, FT, HT, and JT, CH-34, HH-34, SH-34, UH- 34, and VH-34 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-58ET | Airworthiness Directives; SIKORSKY AIRCRAFT Model S-58A, B, C, D, E, F, G, H, J, BT, DT, ET, FT, HT, and JT, CH-34, HH-34, SH-34, UH- 34, and VH-34 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-58F | Airworthiness Directives; SIKORSKY AIRCRAFT Model S-58A, B, C, D, E, F, G, H, J, BT, DT, ET, FT, HT, and JT, CH-34, HH-34, SH-34, UH- 34, and VH-34 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-58FT | Airworthiness Directives; SIKORSKY AIRCRAFT Model S-58A, B, C, D, E, F, G, H, J, BT, DT, ET, FT, HT, and JT, CH-34, HH-34, SH-34, UH- 34, and VH-34 Series Helicopters |
Unsafe Condition
Failure of tail rotor intermediate gearbox input bevel pinions Part Number S1635-64114-0 or output bevel gears Part Number S1635-64115-0.
AI-generated summary from the source AD text. Verify against the official source before acting.
Required Actions
Replace pinions or gears with serviceable parts prior to reaching specified time-in-service limits. For pinions/gears with ≤750 hours by AD effective date, replace before 1,000 hours. For those >750 hours, replace within next 250 hours. Use rotorcraft hours if individual records are unavailable.
AI-generated summary from the source AD text. Verify against the official source before acting.
Compliance Time
Prior to accumulation of 1,000 hours' time in service (for ≤750 hours at effective date) or within next 250 hours' time in service (for >750 hours at effective date).
AI-generated summary from the source AD text. Verify against the official source before acting.
Affected Aircraft
Sikorsky Model S-58A, B, C, D, E, F, G, H, J, BT, DT, ET, FT, HT, JT, CH-34, HH-34, SH-34, UH-34, and VH-34 series helicopters with tail rotor intermediate gearbox using P/N S1635-64114-0 pinions and P/N S1635-64115-0 gears, excluding exempt combinations listed in Note 1.
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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