47-21-09: Hydraulic System Modifications
FAA order 47-21-09 is an airworthiness directive. The FAA's subject line: Hydraulic System Modifications. System: heating, ice protection and utility systems.
What it applies to as the FAA lists it
- Kind of product
- Aircraft
- Makes
- Sierra Hotel Aero, Inc.
- Models
- Navion (Army L-17A)
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 (1,042 characters)
47-21-09 NAVION: (Was Mandatory Note 8 of AD-782-3.) Applies to All Serials Up to and Including Number NAV-4-947.
Compliance required prior to September 1, 1947.
Due to malfunctioning of the hydraulic system which has resulted in the failure of components of that system, including actuating cylinders, the following modifications must be accomplished:
(a) If an engine-driven hydraulic pump is installed in the airplane, rework the hydraulic power system to install the manually controlled relief valve, North American P/N 145- 58027, and replace the existing placard "Hyd. System Pull Off" with new placard "Hyd. Power On".
(North American Field Service Bulletin No. 26 covers this same subject.)
(b) Install the swivel head type nose gear actuating cylinder, North American P/N 145-58014.
(North American Field Service Bulletin No. 19 covers this same subject.)
(c) Visually inspect all flap and landing gear actuating cylinders for evidence of cracks or other damage. Any cylinders found to be damaged should be replaced.
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/47-21-09.json · aircraft systems.