AD 84-25-01
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Sikorsky Aircraft Corporation | S-61A | Airworthiness Directives; SIKORSKY AIRCRAFT DIVISION Model S-61 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-61D | Airworthiness Directives; SIKORSKY AIRCRAFT DIVISION Model S-61 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-61E | Airworthiness Directives; SIKORSKY AIRCRAFT DIVISION Model S-61 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-61L | Airworthiness Directives; SIKORSKY AIRCRAFT DIVISION Model S-61 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-61N | Airworthiness Directives; SIKORSKY AIRCRAFT DIVISION Model S-61 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-61NM | Airworthiness Directives; SIKORSKY AIRCRAFT DIVISION Model S-61 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-61R | Airworthiness Directives; SIKORSKY AIRCRAFT DIVISION Model S-61 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-61V | Airworthiness Directives; SIKORSKY AIRCRAFT DIVISION Model S-61 Series Helicopters |
Unsafe Condition
Failure of either spur gear, part number S6135-20608-1, in the main gearbox could result in loss of main rotor drive system power and subsequent loss of helicopter control.
AI-generated summary from the source AD text. Verify against the official source before acting.
Required Actions
Visually inspect the main gearbox oil scavenge screen or chip detector for steel particles within 10 hours time in service after the effective date and every 10 hours thereafter. Replace the main gearbox before further flight if steel particles are found unless they are fine hairline particles or confirmed as from non-spur gear components. Replace spur gear P/N S6135-20608-1 with P/N S6135-20608-3 and comply with overhaul instructions before December 30, 1986.
AI-generated summary from the source AD text. Verify against the official source before acting.
Compliance Time
within the next 10 hours time in service after the effective date of this AD and thereafter at intervals not to exceed 10 hours time in service from the last inspection
AI-generated summary from the source AD text. Verify against the official source before acting.
Affected Aircraft
Sikorsky Model S-61 series helicopters equipped with Part Number S6135-20608-1 main transmission power input spur gears
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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