# AD 75-12-01: Main Rotor Blades

- Type: Airworthiness directive
- Status: Current
- Products: Sikorsky S-61L, S-61N, S-61NM and S-61R
- Effective: June 12, 1975
- Superseded by: Nothing supersedes this AD
- Product type: Aircraft, Rotorcraft
- Amendment: 39-2221
- Registered aircraft: 48 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/D706F9169267DB7186256A3200694500.0001
- DRS record last changed: May 30, 2024
- Page: https://openairdocs.org/ad/75-12-01

## The airworthiness directive

75-12-01 SIKORSKY AIRCRAFT: Amendment 39-2221. Applies to S-61L, S-61N, S- 61R and S-61NM helicopters certificated in all categories including Military type CH-3C, HH- 3C, CH-3E, and HH-3E helicopters equipped with the following main rotor blades:

  (1) S6115-20501 series, prior to and including S6115-20501-9 main rotor blade assemblies.

  (2) S6115-20601 series, prior to and including S6115-20601-044 main rotor blade assemblies.

  (3) S6117-20101 series, prior to and including S6117-20101-053 main rotor blade assemblies.

  (4) S6188-15001 series, prior to and including S6188-15001-044 main rotor blade assemblies.

Compliance required as indicated.

  (a) Prior to the first flight of each day, inspect each main rotor blade in accordance with Section 2, paragraph C of Sikorsky Service Bulletin No. S61B15-18B or later FAA-approved revisions for possible free counterweights or loose material in the blade spar cavity. If any sound is evident, remove the blade from service immediately and notify Sikorsky Aircraft Product Support Department.

  (b) If any unusual one-per-rev vibration is noted, inspect each main rotor blade prior to further flight for a possible free counter-weight or loose material in the spar cavity in accordance with Section 2, paragraph C of Sikorsky Service Bulletin No. 61B15-18B or later FAA-approved revisions. If any sound is evident, remove the blade from service immediately and notify Sikorsky Aircraft Product Support Department.

  (c) Upon request of the operator, equivalent methods of compliance with the inspection requirements of this AD may be approved by the Chief, Engineering and Manufacturing Branch, New England Region, if the request contains substantiating data to justify that equivalent method for that operator.

This supersedes Amendment 39-1992 (39 F.R. 37356), AD 74-22-02 and Amendment 39-2031 (39 F.R. 41739), AD 74-25-07.

This amendment becomes effective June 12, 1975.

## Affected data sheets (1) (OpenAirDocs)

The type certificate data sheets whose models the AD names.

- [TCDS 1H15](https://openairdocs.org/tcds/1H15): Sikorsky Aircraft; names 4 of 4 models: S-61R, S-61N, S-61L, S-61NM

## Registered aircraft it may apply to (OpenAirDocs)

Matched by airframe and engine model; the AD's applicability may narrow it by serial number, part number or equipment.

- Aircraft: 48 (48 by airframe model, 0 by engine model)
- Makers: Sikorsky 48

Models with the most aircraft:

- [Sikorsky S-61N](https://openairdocs.org/model/sikorsky-s-61n): 45 aircraft (airframe model)
- [Sikorsky S-61L](https://openairdocs.org/model/sikorsky-s-61l): 1 aircraft (airframe model)
- [Sikorsky S-61NM](https://openairdocs.org/model/sikorsky-s-61nm): 1 aircraft (airframe model)
- [Sikorsky S-61R](https://openairdocs.org/model/sikorsky-s-61r): 1 aircraft (airframe model)

All 4 models: https://openairdocs.org/ad/75-12-01/models.md
Every aircraft: https://openairdocs.org/ad/75-12-01/aircraft.md

Its text cites no advisory circulars or STCs.

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