# AD 70-12-04: Main Rotor Shaft Cracks

- Type: Airworthiness directive
- Status: Current
- Products: Sikorsky S-55, S-55B, S-55C and S62A
- Effective: June 17, 1970
- Superseded by: Nothing supersedes this AD
- Product type: Aircraft, Rotorcraft
- Amendment: 39-997
- Registered aircraft: 17 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/ECE7FA7C8948BC2F86256A4D00505F51.0001
- DRS record last changed: May 30, 2024
- Page: https://openairdocs.org/ad/70-12-04

## The airworthiness directive

70-12-04 SIKORSKY ROTORCRAFT: Amdt. 39-997. Applies to S-55, S-55B, S-55C, and S-62A type helicopters certificated in all categories.

Compliance required within the next 15 hours in service after the effective date of this AD, unless already accomplished.

To prevent failure of the main rotor shaft due to fatigue cracks originating from surface conditions, accomplish the following:

  (a) Inspect main rotor shaft P/N S14-35-4308-1, -2, -3 or -4, for cracks and surface conditions in accordance with applicable Sikorsky Service Bulletin No. 55B35-3 or 62B35-10 dated 3 April 1970, or later FAA approved revision, or an equivalent inspection procedure approved by the Chief, Engineering and Manufacturing Branch, FAA Eastern Region.

  (b) Main rotor shafts exhibiting crack indications, or unreworkable surface conditions shall be retired from service prior to further flight and replaced with a shaft which has been inspected in accordance with paragraph (a).

  (c) Main rotor shafts found with reworkable surface conditions may be reworked in accordance with applicable Sikorsky Service Bulletin No. 55B35-3 or 62B35-10 dated 3 April 1970, or later FAA approved revision, or an equivalent rework procedure approved by the Chief, Engineering and Manufacturing Branch, FAA Eastern Region. Should the extent of rework necessitate removal of the shaft from the main gear box, then the replacement shaft must have been inspected in accordance with paragraph (a).

  (d) Upon request of the operator, an FAA maintenance inspector, subject to prior approval of the Chief, Engineering and Manufacturing Branch, FAA Eastern Region may adjust the compliance time specified in this AD if the request contains substantiating data to justify the increase for that operator.

This amendment is effective June 17, 1970.

## Affected data sheets (2) (OpenAirDocs)

The type certificate data sheets whose models the AD names.

- [TCDS 1H4](https://openairdocs.org/tcds/1H4): Centerpointe Aerospace Inc.; names 3 of 3 models: S-55C, S-55, S-55B
- [TCDS 1H13](https://openairdocs.org/tcds/1H13): Centerpointe Aerospace Inc.; names 1 of 1 models: S62A

## 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: 17 (17 by airframe model, 0 by engine model)
- Makers: Sikorsky 15, Sikorsky/Orlando 1, Sikorsky/Vertical 1

Models with the most aircraft:

- [Sikorsky S-55B](https://openairdocs.org/model/sikorsky-s-55b): 9 aircraft (airframe model)
- [Sikorsky S-55](https://openairdocs.org/model/sikorsky-s-55): 3 aircraft (airframe model)
- [Sikorsky S55B](https://openairdocs.org/model/sikorsky-s55b): 3 aircraft (airframe model)
- [Sikorsky/Orlando S-55](https://openairdocs.org/model/sikorsky-orlando-s-55): 1 aircraft (airframe model)
- [Sikorsky/Vertical S-55](https://openairdocs.org/model/sikorsky-vertical-s-55): 1 aircraft (airframe model)

All 5 models: https://openairdocs.org/ad/70-12-04/models.md
Every aircraft: https://openairdocs.org/ad/70-12-04/aircraft.md

Its text cites no advisory circulars or STCs.

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