# AD 51-29-01: Tail Rotor Gearbox Shaft

- Type: Airworthiness directive
- Status: Current
- Products: Scotts-Bell 47 47B, 47B3, 47D and 47D1
- Superseded by: Nothing supersedes this AD
- Product type: Aircraft, Rotorcraft
- Registered aircraft: 54 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/324AB3743DB194F486256A34004E8EBE.0001
- DRS record last changed: May 30, 2024
- Page: https://openairdocs.org/ad/51-29-01

## The airworthiness directive

51-29-01 BELL: Applies to All Models 47B, 47B3, 47D, 47D1 Helicopters.

Compliance required as indicated.

1. Replace the tail rotor gearbox shaft, P/N 47-645-028-1 or 47-645-051-1, when it has accumulated 900 hours of operation.

2. Any shaft having already accumulated 900 hours of operation must be replaced by February 1, 1952. In the interim, conduct the following inspection after every 25 hours of operation: Remove tail rotor and inspect attachment bolt hole for cracks. Replace the shaft if a crack is found, or the hole is elongated over 0.010 inch.

(Bell Service Bulletin No. 83 covers this same subject.)

## Affected data sheets (1) (OpenAirDocs)

The type certificate data sheets whose models the AD names.

- [TCDS H-1](https://openairdocs.org/tcds/H-1): Scott's-Bell 47 Inc; names 4 of 9 models: 47B, 47B3, 47D1, 47D

## 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: 54 (54 by airframe model, 0 by engine model)
- Makers: Bell 52, Bell Kitz Kopters 1, Bell-Allied Helicopter 1

Models with the most aircraft:

- [Bell 47D1](https://openairdocs.org/model/bell-47d1): 47 aircraft (airframe model)
- [Bell 47D](https://openairdocs.org/model/bell-47d): 4 aircraft (airframe model)
- [Bell 47B](https://openairdocs.org/model/bell-47b): 1 aircraft (airframe model)
- [Bell Kitz Kopters 47D1](https://openairdocs.org/model/bell-kitz-kopters-47d1): 1 aircraft (airframe model)
- [Bell-Allied Helicopter 47D1](https://openairdocs.org/model/bell-allied-helicopter-47d1): 1 aircraft (airframe model)

All 5 models: https://openairdocs.org/ad/51-29-01/models.md
Every aircraft: https://openairdocs.org/ad/51-29-01/aircraft.md

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.