# AD 77-04-06: Main Rotor Gearbox

- Type: Airworthiness directive
- Status: Historical
- Products: Airbus Helicopters Deutschland BO-105A and BO-105C
- Effective: August 23, 1979
- Published: February 17, 1977
- Issued: February 7, 1977
- Superseded by: [AD 2022-24-07](https://openairdocs.org/ad/2022-24-07)
- Product type: Aircraft, Rotorcraft
- Amendment: 39-2835
- Registered aircraft: 4 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/9B6B60482541989986256A3A006E1A15.0001
- DRS record last changed: November 21, 2025
- Page: https://openairdocs.org/ad/77-04-06

## The airworthiness directive

77-04-06 MESSERSCHMITT-BOLKOW-BLOHM (MBB): Amendment 39-2835 as amended by amendment 39-3528. Applies to all Model BO-105A and BO-105C helicopters, certificated in all categories. Compliance is required as indicated. To prevent the possible failure of a main rotor gearbox support, P/Ns 105-10161 and 105-10162, replace the two supports with serviceable supports within the next 10 hours time in service after the effective date of this AD or prior to the accumulation of 6,800 hours time in service on the supports, whichever occurs later, and, thereafter, continue to replace the supports prior to the accumulation of 6,800 hours time in service. Amendment 39-2835 became effective March 3, 1977. This amendment 39-3528 becomes effective August 23, 1979.

## Affected data sheets (1) (OpenAirDocs)

The type certificate data sheets whose models the AD names.

- [TCDS H3EU](https://openairdocs.org/tcds/H3EU): Airbus Helicopters Deutschland GmbH (AHD); names 2 of 5 models: BO-105C, BO-105A

## 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: 4 (4 by airframe model, 0 by engine model)
- Makers: Messerschmitt-Boelkow-Blohm-Gm 4

Models with the most aircraft:

- [Messerschmitt-Boelkow-Blohm-Gm BO-105C](https://openairdocs.org/model/messerschmitt-boelkow-blohm-gm-bo-105c): 4 aircraft (airframe model)

All 1 models: https://openairdocs.org/ad/77-04-06/models.md
Every aircraft: https://openairdocs.org/ad/77-04-06/aircraft.md

## Related documents

- [AD 2022-24-07](https://openairdocs.org/ad/2022-24-07): Main Rotor Drive System · ECD Superlifter Conversion Kit 105-800331 (Eurocopter Deutschland STC SR00043RD). Effective Jan 6, 2023. Supersedes this AD

Its text cites no advisory circulars or STCs.

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