Power brakes are operated using pressure from the ______ hydraulic system.

• A. Auxiliary
• B. Main
• C. Emergency
• D. Secondary

Answer: (B)

Power brakes rely on a ready supply of high-pressure hydraulic fluid to push the brake pistons in the wheel brakes. That pressure comes from the main hydraulic system. When you apply the brakes, the input moves valves and directs fluid from the main system to the wheel brake actuators, squeezing the pads against the rotors and slowing the airplane. Other hydraulic networks (auxiliary, secondary, emergency) exist to power different systems or to provide backup pressure, but for normal braking the primary source is the main hydraulic system. If the main system were unavailable, some aircraft can use an emergency system for limited braking, but the normal operation depends on the main hydraulic system.