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This aerospace information report (AIR) provides historical design information for various aircraft landing gear and actuation/control systems that may be useful in the design of future systems for similar applications. It presents the basic characteristics, hardware descriptions, functional schematics, and discussions of the actuation mechanisms, controls, and alternate release systems. The report is divided into two basic sections: 1 Landing gear actuation system history from 1876 to the present. This section provides an overview and the defining examples that demonstrate the evolution of landing gear actuation systems to the present day. 2 This section of the report provides an in depth review of various aircraft. A summary table of aircraft detail contained within this section is provided in paragraph 4.1. The intent is to add new and old aircraft retraction/extension systems to this AIR as the data becomes available.

CPs are a process that is executed on a critical landing gear (or undercarriage) part, assembly or equipment that if performed incorrectly or omitted would cause: An operational failure of the aircraft; or An unacceptable risk of injury This document identifies CPs that have either caused operational failure or that can be reasonably expected to cause operational failures based on experience. Note that in the interest of brevity, that this document is not intended to be a definitive listing, only an introduction and a consideration of common processes.

This document establishes a procedure for disposition of landing gear components that have been involved in accidents/incidents. The recommendations in this document apply to components made of ferrous and non-ferrous alloys. The recommendations in this document do not apply to components made of non metallic composite materials.

This information report provides general guidance for the design considerations, qualification in endurance, strength and fatigue of landing gear using composite components as principle structural elements. The information discussed herein includes the development and evaluation of design data considering: the potential for imbedded manufacturing defects, manufacturing process variations, the component operating environment, potential damage threats in service, rework and overhaul, and inspection processes. This AIR mainly discusses the use of thick composites for landing gear structural components. Considerations and recommendations provided in this AIR may therefore differ greatly from considerations and recommendations found in widely accepted composite design references such as CMH-17 and Advisory Circulars such as AC 20-107(B).

The intent of this AIR is twofold: (1) to present descriptive summary of aircraft nosewheel steering and centering systems, and (2) to provide a discussion of problems encountered and “lessons learned” by various airplane manufacturers and users. This document covers both military aircraft (land-based and ship-based) and commercial aircraft. It is intended that the document be continually updated as new aircraft and/or new “lessons learned” become available.

This document outlines the most common repairs used on landing gear components. It is not the intention of this AIR to replace overhaul/component maintenance or technical order manuals, but it can serve as a guide into their preparation. Refer to the applicable component drawings and specifications for surface finish, thickness, and repair processing requirements. This document may also be used as a guide to develop an MRB (Material Review Board) plan. The repairs in this document apply to components made of metallic alloys. These repairs are intended for new manufactured components and overhauled components, including original equipment manufacturer (OEM)/depot and in-service repairs. The extent of repair allowed for new components as opposed to in-service components is left to the cognizant engineering authorities. Reference could be made to this document when justifying repairs on landing gears. For repairs outside the scope of this document, a detailed justification is necessary.

This document defines the criteria used for the selection of landing gear shock strut upper and lower bearings (see Figure 1).

This document is intended to give advisory information for the selection of plain bearings and bearing materials most suitable for aircraft landing gear applications. Information included herein was derived from bearing tests and service experience/reports. Airframe/landing gear manufacturers, commercial airlines, the U.S. Air Force and Naval Air Systems Command provided input for the document. Information is given on bearing installation methods and fits that have given satisfactory performance and service life. Base metal corrosion is a major cause of problems in bearing installations for landing gears. Therefore, methods of corrosion prevention are discussed. Effort is directed toward minimizing maintenance and maximizing life expectancy of landing gear bearings. Lubricated and self-lubricating bearings are also discussed. There are wide ranges of bearing load and motion requirements for applications in aircraft landing gears.

This document outlines the most common repairs used on landing gear components. It is not the intention of this AIR to replace Overhaul/Component Maintenance or Technical Order Manuals, but it can serve as a guide into their preparation. This document may also be used as a template to develop an MRB (Material Review Board) plan. The recommendations in this document apply to components made of metallic alloys. These recommendations are intended for new manufactured components as well as for overhauled components. The extent of repair allowed for new components as opposed to in-service components is left to the cognizant engineering authorities. Reference could be made to this document when justifying repairs on landing gears. For repairs outside the scope of this document, a detailed justification is necessary. It must be understood that all the repairs listed in this document are not to be applied without the involvement of the cognizant engineer.

A landing gear system comprises the most compelling assembly of engineering skills. Its importance to the successful design of an aircraft can be favorably compared with that of the aircraft's wings and engines. A landing gear system consists of several different engineering disciplines, and is continually in the public eye especially with regard to safety. The primary objective of AIR4846 is to present a record of a variety of interesting gears, gear/aircraft systems and patents, and to discuss wherever possible the lessons learned, and the reasons for the design. Thus, the document is not only a historical account, but a means of recording technical knowledge for the practical benefit of future landing gear designers. Commendable efforts have been made over the years by several individuals to make such recordings, and AIR4846 will make continual reference to them. This applies to all books, papers, or specifications that have the approval of the SAE A-5 Committee.

This SAE Aerospace Information Report (AIR) advises that some of the chemicals being used to disinfect, de-ice, and clean airplanes can cause corrosion and/or degradation of landing gear components. Landing gear equipment includes shock struts, braces, actuators, wheels, brakes, tires, and electrical components. Some of the chemicals that have been recognized as potentially injurious are identified and recommendations for mitigating damage are presented.

This specification contains landing gear strength and rigidity requirements, which, in combination with other applicable specifications, define the structural design, analysis, test, and data requirements for fixed wing piloted airplanes. These requirements include, but are not limited to the following: a General Specifications 1 The shock-absorption characteristics and strength of landing-gear units and the strength and rigidity of their control systems and of their carry-through structures.

This document provides recommended practices for the design, development, and verification testing of aircraft nosewheel steering (NWS) systems.

This SAE Aerospace Recommended Practice (ARP) applies to fatigue testing of landing gear and landing gear components.

This document defines the criteria used for the selection of landing gear shock strut upper and lower bearings.

This specification contains landing gear strength and rigidity requirements, which, in combination with other applicable specifications, define the structural design, analysis, test, and data requirements for fixed wing piloted airplanes. These requirements include, but are not limited to the following: a General Specifications 1 The shock-absorption characteristics and strength of landing-gear units and the strength and rigidity of their control systems and of their carry-through structures.

This document covers both military aircraft (land-based and ship-based) and commercial aircraft. It is intended that the document be continually updated as new aircraft and/or new "lessons learned" become available.

This document establishes a procedure for disposition of landing gear components that have been involved in accidents/incidents. The recommendations in this document apply to components made of ferrous and non-ferrous alloys.

Recent field experience has indicated significant problems with some types of wire and cable as routed on aircraft landing gear. This Aerospace Information Report (AIR) is intended to identify environmental concerns the designer must consider, materials that appear to be most suitable for use in these areas, routing, clamping, and other protection techniques that are appropriate in these applications.