# AD 77-21-01: Tail Rotor Gear Boxes - Type: Airworthiness directive - Status: Current - Products: Scotts-Bell 47 47, 47B, 47B3, 47D, 47D1, 47E, 47G, 47G-2, 47G-2A, 47G-2A-1, 47G-3, 47G-3B and 12 more - Effective: November 14, 1977 - Superseded by: Nothing supersedes this AD - Product type: Aircraft, Rotorcraft - Amendment: 39-3054 - Registered aircraft: 490 may be affected, by airframe or engine model (OpenAirDocs) - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/DE93B1F0890151D186256A340054ED09.0001 - DRS record last changed: May 30, 2024 - Page: https://openairdocs.org/ad/77-21-01 ## The airworthiness directive 77-21-01 BELL HELICOPTER TEXTRON: Amendment 39-3054. Applies to all Model 47 helicopters with tail rotor gear boxes, part number 47-640-075-1 or 47-640-075-5, installed. NOTE: Retrofit kits incorporating these gear boxes or the associated internal gears and bearings delivered from Bell Helicopter Textron after December 1, 1976, have been verified to be in compliance with this airworthiness directive and will not require inspection and/or further retrofit. Compliance is required within the next 100 hours time in service after the effective date of this Airworthiness Directive, unless already accomplished. To minimize the possibility of loss of directional control of the helicopter resulting from failure of the bearing, part number 47-620-629-3 or 47-620-629-5, or failure of the input pinion shaft, part number 47-645-205-3, located in the tail rotor gear box, part number 47-640-075-1 or 47-640-075-7, conduct the inspection and replacement activities prescribed by paragraphs 1, 2, 2a, 2b, 3, and 4 of Bell Helicopter Textron Service Bulletin No. 47-77-1, dated February 14, 1977, or later FAA approved revision. Comments in paragraph 5 and 6 of this bulletin involving warranties, replacement part sources, or reporting activities, are not a part of this Airworthiness Directive. After accomplishment of paragraphs 1, 2, 3, and 4 of Service Bulletin No. 47-77-1, reassemble and reinstall the tail rotor gear box in accordance with the Maintenance and Overhaul Instruction for the applicable model helicopters. The manufacturer's specifications and procedures identified and described in this directive are incorporated herein and made a part hereof, pursuant to 5 U.S.C. 552(a)(1). All persons affected by this directive, who have not already received these documents from the manufacturer, may obtain copies by requesting same from Service Manager, Bell Helicopter Textron, P.O. Box 482, Fort Worth, Texas, 76101. These documents may also be examined at Officeof the Regional Counsel, Southwest Region, Federal Aviation Administration, 4400 Blue Mound Road, Fort Worth, Texas, 76106, and the Federal Aviation Administration Headquarters, 800 Independence Avenue, S.W., Washington, D.C., 20591. Equivalent means of compliance with the modifications prescribed by this Airworthiness Directive may be approved by the Chief, Engineering and Manufacturing Branch, Flight Standards Division, Southwest Region, Federal Aviation Administration, P.O. Box 1689, Fort Worth, Texas, 76101. This amendment becomes effective November 14, 1977. ## Affected data sheets (3) (OpenAirDocs) The type certificate data sheets whose models the AD names. - [TCDS 2H3](https://openairdocs.org/tcds/2H3): Scott's-Bell 47 Inc; names 11 of 11 models: 47G-2A, 47G-3B, 47G-3, 47G-4A, 47G-5A, 47G-5, 47G-3B-2A, 47G-3B-2… - [TCDS H-1](https://openairdocs.org/tcds/H-1): Scott's-Bell 47 Inc; names 9 of 9 models: 47H-1, 47B, 47B3, 47D1, 47D, 47G-2, 47G, 47… - [TCDS 2H1](https://openairdocs.org/tcds/2H1): Scott's-Bell 47 Inc; names 4 of 4 models: 47K, 47J-2, 47J-2A, 47J ## 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: 490 (490 by airframe model, 0 by engine model) - Makers: Bell 476, Bell-K-Copter 3, Bell Kitz Kopters 1, Bell-Allied Helicopter 1, Bell-Carson 1, Bell-Huddleston And Wilson 1, Bell-Intermountain 1, Bell-Olympic Helicopters 1, Bell-Shippey 1, Bell-Tellijohn 1 Models with the most aircraft: - [Bell 47G-2](https://openairdocs.org/model/bell-47g-2): 87 aircraft (airframe model) - [Bell 47G-3B-1](https://openairdocs.org/model/bell-47g-3b-1): 86 aircraft (airframe model) - [Bell 47G](https://openairdocs.org/model/bell-47g): 55 aircraft (airframe model) - [Bell 47D1](https://openairdocs.org/model/bell-47d1): 47 aircraft (airframe model) - [Bell 47G-5](https://openairdocs.org/model/bell-47g-5): 40 aircraft (airframe model) - [Bell 47G-3B-2](https://openairdocs.org/model/bell-47g-3b-2): 26 aircraft (airframe model) - [Bell 47G-4A](https://openairdocs.org/model/bell-47g-4a): 20 aircraft (airframe model) - [Bell 47G-2A](https://openairdocs.org/model/bell-47g-2a): 19 aircraft (airframe model) - [Bell 47G-5A](https://openairdocs.org/model/bell-47g-5a): 19 aircraft (airframe model) - [Bell 47G-3B](https://openairdocs.org/model/bell-47g-3b): 15 aircraft (airframe model) - [Bell 47G-2A-1](https://openairdocs.org/model/bell-47g-2a-1): 13 aircraft (airframe model) - [Bell 47G-4](https://openairdocs.org/model/bell-47g-4): 13 aircraft (airframe model) - [Bell 47G3B2A](https://openairdocs.org/model/bell-47g3b2a): 7 aircraft (airframe model) - [Bell 47H-1](https://openairdocs.org/model/bell-47h-1): 6 aircraft (airframe model) - [Bell 47J](https://openairdocs.org/model/bell-47j): 6 aircraft (airframe model) - [Bell 47J-2](https://openairdocs.org/model/bell-47j-2): 6 aircraft (airframe model) - [Bell 47J-2A](https://openairdocs.org/model/bell-47j-2a): 5 aircraft (airframe model) - [Bell 47D](https://openairdocs.org/model/bell-47d): 4 aircraft (airframe model) - [Bell-K-Copter 47G](https://openairdocs.org/model/bell-k-copter-47g): 2 aircraft (airframe model) - [Bell 47B](https://openairdocs.org/model/bell-47b): 1 aircraft (airframe model) All 35 models: https://openairdocs.org/ad/77-21-01/models.md Every aircraft: https://openairdocs.org/ad/77-21-01/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.