52-21-01: Lord Mount Guards
FAA order 52-21-01 is an airworthiness directive. The FAA's subject line: Lord Mount Guards. It names Bell 47: about 478 aircraft on the U.S. register today, though an order usually covers particular versions or serial numbers rather than every one. System: other and general.
What it applies to as the FAA lists it
- Kind of product
- Aircraft
- Makes
- Scotts-Bell 47 Inc
- Models
- 47, 47B, 47B3, 47D, 47D1, 47E, 47G, 47G-2, 47G-2A, 47G-2A-1, 47G-3, 47G-3B, 47G-3B-1, 47G-3B-2, 47G-3B-2A, 47G-4, 47G-4A, 47G-5, 47G-5A, 47H-1, 47J, 47J-2, 47J-2A, 47K
- On this site
- Bell 47 478 registered
Dates and paperwork
- Docket
- Unknown
- Status
- Current
- The FAA's document
- Read the order on the FAA's site
The order itself the regulatory text, as published
Show the full text (1,172 characters)
52-21-01 BELL: Applies to Model 47 Helicopters as Noted Below.
Compliance required by October 15, 1952.
To prevent engine mount shifting on the rubber Lord mounts, the following applicable Lord mount guards must be installed:
1. 178 H. P. Engines - Models 47B, 47B3, and 47D Helicopters. If not already incorporated, install two 47-612-123-1 guards on engine mount. When properly installed, a 5/32 inch torque offset exists between engine mount clamp and rubber Lord mount. This offset is at the rearward side of right hand Lord mount and the forward side of left hand Lord mount.
2. 200 H. P. Engines - All Model 47 Helicopters. Inspect the two 47-612-123-3 guards to be sure they have 7/32 inch ears. If no guards are installed or the ears are less than 3/16 inch they must be replaced with the new type guards. When properly installed, a 1/4 inch torque offset exists between engine mount clamp and rubber Lord mount. This offset is at the rearward side of right hand Lord mount and the forward side of left hand Lord mount.
(Bell Service Bulletin No. 79, Revision A, dated July 7, 1952, covers this same subject.)
This supersedes AD 52-01-04.
Related safety bulletins advice on the same designs, not orders
2001-02-09SW-01-13 ·
Source: FAA Dynamic Regulatory System, airworthiness directives. The FAA's document is the authority; the register counts are this site's, from the FAA register of November 6, 2026. Connections as data: /graph/directive/52-21-01.json · aircraft systems.