How does the parking brake differ from the regular brake system in terms of hydraulic circuits?

• A. Parking brake typically locks the hydraulic lines or a separate circuit to hold pressure and prevent release, often with a lock or mechanical pawl; regular brakes use pedal pressure to apply hydraulic pressure.
• B. Parking brake uses an electric motor to apply brakes; regular brakes are hydraulic only.
• C. Parking brake uses pneumatic pressure; regular brakes use hydraulic pressure.
• D. Parking brake is not connected to the hydraulic system and only uses mechanical force from a lever.

Answer: (A)

The main idea is that the parking brake is designed to hold the brakes applied by isolating or locking a portion of the hydraulic system so pressure can be maintained without ongoing pedal input. When you activate the parking brake, a dedicated valve or mechanism traps hydraulic pressure in the brake lines (often with a mechanical lock or pawl), creating a stored pressure hold that prevents the brakes from releasing. This lets the aircraft stay parked even if the main hydraulic pressure varies or drops.

Regular brakes, by contrast, rely on you pressing the brake pedal to create hydraulic pressure through the master cylinder and into the brake actuators. Once you release the pedal, that pressure is no longer sustained, and the brakes release. The parking brake’s ability to lock or isolate pressure is what sets it apart from the normal braking path.

Options that suggest electric actuation, pneumatic pressure, or having no hydraulic connection don’t reflect how a parking brake functions in this context, since the essential feature is the separate circuit or locking mechanism that holds pressure to keep the brakes applied.