AD 90-01-04
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Sikorsky Aircraft Corporation | S-61A | Airworthiness Directives; Sikorsky Aircraft Model S-61 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-61D | Airworthiness Directives; Sikorsky Aircraft Model S-61 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-61E | Airworthiness Directives; Sikorsky Aircraft Model S-61 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-61L | Airworthiness Directives; Sikorsky Aircraft Model S-61 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-61N | Airworthiness Directives; Sikorsky Aircraft Model S-61 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-61NM | Airworthiness Directives; Sikorsky Aircraft Model S-61 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-61R | Airworthiness Directives; Sikorsky Aircraft Model S-61 Series Helicopters |
| aircraft | Sikorsky Aircraft Corporation | S-61V | Airworthiness Directives; Sikorsky Aircraft Model S-61 Series Helicopters |
Unsafe Condition
Failure of the main rotor hub upper plate, which could result in the loss of the helicopter.
AI-generated summary from the source AD text. Verify against the official source before acting.
Required Actions
Conduct a one-time inspection of the main rotor head with bifilar assembly, including loosening bolts, checking clearance with a 0.010-inch feeler gauge, reshimming if necessary, and torque to 1,690 inch-pounds. Inspect for cracks in hub upper plate arm bifilar attachment bolt holes and adjacent surfaces; use dye penetrant if cracks are found, and replace the main rotor hub assembly if verified. Operators may seek alternate compliance methods approved by the Boston Aircraft Certification Office.
AI-generated summary from the source AD text. Verify against the official source before acting.
Compliance Time
within the next 150 hours' time in service after the effective date of this AD, unless already accomplished
AI-generated summary from the source AD text. Verify against the official source before acting.
Affected Aircraft
Sikorsky Model S-61 series helicopters with part number S6110-23300 main rotor head.
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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