A panel of the SAE A-5A Committee prepared this SAE Aerospace Information Report (AIR). Thedocument describes the design approaches used for current applications of Brake-by-Wire (BBW)control systems that are used on commercial and military airplanes. The document also discusses theexperience gained during service in the commercial and military environments, and covers system,ergonomic, hardware, and development aspects. The treatment includes the lessons that have beenlearned during application of the technology.Although there are a variety of approaches that have been used in the design of BBW systems, themain focus of this document is on systems that use the electro-hydraulic method of control. Theoverall range of implementations is briefly described in 2.3. Sections 3, 4, and 5 describe the electrohydraulic method in detail.1.1 Purpose:Although the designers and users of BBW systems are familiar with their functions, features,components, and limitations, there is no readily available documentation that describes the field inbreadth. This document seeks to address this need by providing a compendium of field experience.The experience that has accumulated from existing BBW systems is presented as an aid to thosewho are embarking on the design of a new application or who are preparing specifications for a BBWsystem. The information is arranged under the headings of Functions and Requirements, SystemArchitecture, Hardware Components, System Development Process, and Lessons Learned.1.2 Introduction:Aircraft braking systems provide the pilot with a means of controlling the deceleration of the airplane through the use of brake pedals. Before the advent of BBW systems, aircraft braking systems usedhydraulically actuated brakes that are connected to brake pedals through mechanical cables, statichydraulic systems or linkages. In BBW systems, electrical wires replace the mechanical linkages.Electrical sensors are used to measure the pilot’s command at the brake pedals and an ElectricalControl Unit (ECU) sends out signals to the electro-hydraulic components that control braking force.The other main functions that are provided by an aircraft braking system, independently of whether itis BBW or mechanically operated, are antiskid, autobrake, and parking brake.BBW systems are generally required to have a redundant means of applying brakes. Thesealternate braking or emergency braking systems usually rely on the mechanical levers and linkagesthat they seek to eliminate, although some purely electrical BBW systems are beginning to appear.In addition to the traditional electro-hydraulic brake actuation methods, there have been somedemonstrations of “all electric” brake systems that use electromechanical brake actuators, but theyfall outside the scope of this document.The components used in existing BBW systems and the way that they are combined to form systemarchitectures that meet the requirements for safety and reliability are described in this document.