# AD 56-21-01: Hydraulic Boost Cylinders

- Type: Airworthiness directive
- Status: Current
- Products: Scotts-Bell 47 47G, 47G-2 and 47H-1
- Superseded by: Nothing supersedes this AD
- Product type: Aircraft, Rotorcraft
- Registered aircraft: 158 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/F89A62D08F669E0486256A34004F932A.0001
- DRS record last changed: May 30, 2024
- Page: https://openairdocs.org/ad/56-21-01

## The airworthiness directive

56-21-01 BELL: Applies to All Models 47G, 47G2, and 47H1 Helicopters Except As Noted Below and All Spare Hydraulic Boost Power Cylinders Part Numbers 1090, 1190 and All 1270 Cylinders Prior to and Including Serial Number 733. Model 47G, Serial Numbers 1530 and 1687 and Up; Model 47G2, Serial Numbers 1494, 1505, 1506, 1508, 1617 and Up; and Model 47H1, Serial Numbers 1534 and Up Will be Modified Prior to Delivery.

Compliance required as indicated.

Malfunctioning of the hydraulic boost cylinder in service has necessitated the replacement of the hydraulic boost power cylinder barrels and clamps in the fore and aft and lateral cyclic boost power cylinder units and the establishment of a service life of 100 hours on the cylinders which have not been modified. These hydraulic boost cylinder barrels must be replaced by the time 100 hours service is obtained, except barrels that have already accumulated 100 hours service prior to the date of this directive may be used until 125hours are obtained or until December 1, 1956, whichever occurs first.

(Detail procedures for installation of cylinder barrel P/N 1097 and clamps P/N 1029 are contained in Bell's Mandatory Service Bulletin No. 114 dated August 27, 1956.)

## 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 3 of 9 models: 47H-1, 47G-2, 47G

## 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: 158 (158 by airframe model, 0 by engine model)
- Makers: Bell 148, Bell-K-Copter 3, Bell-Carson 1, Bell-Olympic Helicopters 1, Bell-Shippey 1, Bell-Tellijohn 1, Bell-Transworld Helicopter Cor 1, Bell-Yehnert 1, Continental Copters 1

Models with the most aircraft:

- [Bell 47G-2](https://openairdocs.org/model/bell-47g-2): 87 aircraft (airframe model)
- [Bell 47G](https://openairdocs.org/model/bell-47g): 55 aircraft (airframe model)
- [Bell 47H-1](https://openairdocs.org/model/bell-47h-1): 6 aircraft (airframe model)
- [Bell-K-Copter 47G](https://openairdocs.org/model/bell-k-copter-47g): 2 aircraft (airframe model)
- [Bell-Shippey BELL 47G](https://openairdocs.org/model/bell-shippey-bell-47g): 1 aircraft (airframe model)
- [Bell-Carson 47G](https://openairdocs.org/model/bell-carson-47g): 1 aircraft (airframe model)
- [Bell-Tellijohn 47G-2](https://openairdocs.org/model/bell-tellijohn-47g-2): 1 aircraft (airframe model)
- [Bell-K-Copter 47G-2](https://openairdocs.org/model/bell-k-copter-47g-2): 1 aircraft (airframe model)
- [Bell-Transworld Helicopter Cor 47G-2](https://openairdocs.org/model/bell-transworld-helicopter-cor-47g-2): 1 aircraft (airframe model)
- [Bell-Olympic Helicopters 47G2](https://openairdocs.org/model/bell-olympic-helicopters-47g2): 1 aircraft (airframe model)
- [Bell-Yehnert 47G-2](https://openairdocs.org/model/bell-yehnert-47g-2): 1 aircraft (airframe model)
- [Continental Copters 47G](https://openairdocs.org/model/continental-copters-47g): 1 aircraft (airframe model)

All 12 models: https://openairdocs.org/ad/56-21-01/models.md
Every aircraft: https://openairdocs.org/ad/56-21-01/aircraft.md

Its text cites no advisory circulars or STCs.

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