Figure 13-103.  The location of a brake debooster cylinder on a landing gear strut and the debooster’s position in relation to other  components of a power brake system.  Emergency brake valve Hydraulic system pressure Emergency IR cylinder Air/oil transfer tube Brake accumulator Brake debooster Brake debooster Brake check valve Power brake control valves Antiskid control valves Deboosters Shuttle valves Brake assemblies Air pressure Hydraulic pressure Deboost pressure Hydraulic return not happen, each wheel is monitored for a deceleration rate  faster than a preset rate. When excessive deceleration is  detected, hydraulic pressure is reduced to the brake on that  wheel. To operate the anti-skid system, flight deck switches  must be placed in the ON position.  [Figure 13-105]  After the  aircraft touches down, the pilot applies and holds full pressure  to the rudder brake pedals. The anti-skid system then functions  automatically until the speed of the aircraft has dropped to  approximately 20 mph. The system returns to manual braking  mode for slow taxi and ground maneuvering.  There are various designs of anti-skid systems. Most contain  three main types of components: wheel speed sensors, anti- skid control valves, and a control unit. These units work  together without human interference. Some anti-skid systems  provide complete automatic braking. The pilot needs only to  turn on the auto brake system, and the anti-skid components  slow the aircraft without pedal input.  [Figure 13-105]  Ground  safety switches are wired into the circuitry for anti-skid and  auto brake systems. Wheel speed sensors are located on each  wheel equipped with a brake assembly. Each brake also has  Large aircraft with power brakes require anti-skid systems.  It is not possible to immediately ascertain in the flight deck  when a wheel stops rotating and begins to skid, especially in  aircraft with multiple-wheel main landing gear assemblies. A  skid not corrected can quickly lead to a tire blowout, possible  damage to the aircraft, and control of the aircraft may be lost. The anti-skid system not only detects wheel skid, it also  detects when wheel skid is imminent. It automatically relieves  pressure to the brake pistons of the wheel in question by  momentarily connecting the pressurized brake fluid area to the  hydraulic system return line. This allows the wheel to rotate  and avoid a skid. Lower pressure is then maintained to the  brake at a level that slows the wheel without causing it to skid. Maximum braking efficiency exists when the wheels are  decelerating at a maximum rate but are not skidding. If a  wheel decelerates too fast, it is an indication that the brakes  are about to lock and cause a skid. To ensure that this does  13-61 Anti-Skid System Operation