One of the most difficult tasks regarding aircraft brakes is that of "bleeding" or eliminating air from the braking system, which ensures proper brake operation. I will discuss hydraulic brake operation and specifically the procedures for eliminating air from the brake system and how to prevent air or dirt from entering during maintenance. Before getting into the process of bleeding it is important to understand how the system works and the basic design of an aircraft hydraulic brake system. I will be discussing brake systems on the typical light aircraft that have no power assist and use aircraft standard petroleum base hydraulic fluid. This is an important distinction from that of automotive systems that are generally power assisted and use a fluid that is not petroleum based. Never use automotive brake fluid in any aircraft hydraulic system including the brakes as the fluids are not interchangeable and will destroy elastic seals in hydraulic components.
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