Abstract: An aircraft brake system includes a supply line for supplying hydraulic fluid to wheel brakes, and an associated return line. Hydraulic fluid is replenished in at least a portion of the return line both before applying a braking force to the one or more wheels of the aircraft during landing, and before an intervening, optional, step if so performed of testing the brake system before landing of the aircraft. Replenishing the hydraulic fluid can be conducted by a control unit automatically and/or in response to a pressure drop in the return line measure by a transducer.

Abstract: A hydraulic brake system for activating the wheel brakes of an aircraft landing gear assembly includes a hydraulic fluid supply line and an associated return line. There is a valve which separates a source of hydraulic fluid from a portion of the return line and an associated leak path associated with the valve that in use maintains the pressure and/or volume of hydraulic fluid in the portion of the return line above a minimum acceptable level. The leak path may be provided by a hole drilled in a part (e.g. the poppet) of a non-return check valve.