# AD 77-20-01: Main Transmission Lower Planetary Plates

- Type: Airworthiness directive
- Status: Historical
- Products: Erickson Air-Crane S-64E and S-64F
- Superseded by: [AD 97-19-10](https://openairdocs.org/ad/97-19-10)
- Product type: Aircraft, Rotorcraft
- Amendment: 39-3064
- Registered aircraft: 22 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/BE77AA277C0F649186256A560049A8B9.0001
- DRS record last changed: August 7, 2025
- Page: https://openairdocs.org/ad/77-20-01

## The airworthiness directive

77-20-01 SIKORSKY AIRCRAFT: Amendment 39-3045 as amended by Amendment 39- 3064. Applies to all Sikorsky Model S-64E and S-64F helicopters. Compliance required as indicated, unless already accomplished.

1. To prevent cracking and possible failure of main transmission lower planetary plates, P/N 6435-20229-102, inspect for cracks in accordance with Sikorsky Service Bulletin No. 64B35-7 prior to the accumulation of 1300 hours time in service, or within the next 30 hours time in service after receipt of this telegram, whichever is later, and every 70 hours time in service thereafter. Cracked plates must be removed before further flight.

2. Effective October 30, 1977, P/N 6435-20229-102 plates with 2000 or more hours total time in service must be removed from service.

3. For P/N 6435-20229-102 plates with 1300 or more hours total time in service after receipt of this telegram, inspect main transmission oil filter pack daily for magnesium chips. If chips are found, remove main transmission from service before further flight.

4. In lieu of Paragraphs 1, 2, and 3 above, plates may be inspected, reworked, and reidentified as P/N 6435-20229-102-TS-107 in accordance with Sikorsky Service Bulletin 64B35-7A or later FAA approved revisions.

5. Reworked plates, P/N 6435-20229-102-TS-107, shall be retired prior to the accumulation of 2,600 hours total time in service.

Upon request of the operator, an FAA maintenance inspector, subject to prior approval of the Chief, Engineering and Manufacturing Branch, FAA, New England Region, may adjust the repetitive inspection intervals specified in this AD to permit compliance at an established inspection period of the operator if the request contains substantiating data to justify the increase for that operator.

Sikorsky Alert Service Bulletin No. 64B35-7 refers to this subject.

Amendment 39-3045 became effective upon receipt of telegraphic AD for all operators which received notice by telegraphicAD and became effective upon publication in the Federal Register for all others.

This amendment 39-3064 becomes effective upon publication in the Federal Register.

## Affected data sheets (1) (OpenAirDocs)

The type certificate data sheets whose models the AD names.

- [TCDS H6EA](https://openairdocs.org/tcds/H6EA): Erickson Incorporated DBA Erickson Air-Crane; names 1 of 2 models: S-64F

## 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: 22 (22 by airframe model, 0 by engine model)
- Makers: Sikorsky 16, Erickson 5, Erickson Air Crane 1

Models with the most aircraft:

- [Sikorsky S-64E](https://openairdocs.org/model/sikorsky-s-64e): 11 aircraft (airframe model)
- [Sikorsky S-64F](https://openairdocs.org/model/sikorsky-s-64f): 5 aircraft (airframe model)
- [Erickson S64E](https://openairdocs.org/model/erickson-s64e): 4 aircraft (airframe model)
- [Erickson S-64F](https://openairdocs.org/model/erickson-s-64f): 1 aircraft (airframe model)
- [Erickson Air Crane S-64E](https://openairdocs.org/model/erickson-air-crane-s-64e): 1 aircraft (airframe model)

All 5 models: https://openairdocs.org/ad/77-20-01/models.md
Every aircraft: https://openairdocs.org/ad/77-20-01/aircraft.md

## Related documents

- [AD 97-19-10](https://openairdocs.org/ad/97-19-10) (historical): Main Transmission Plates Inspection · Erickson Air-Crane S-64E. Effective Oct 17, 1997. Supersedes this AD

Its text cites no advisory circulars or STCs.

---
OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.