What is the function of the parking brake in most aircraft?

• A. To power the landing gear extension.
• B. To release the landing gear lock.
• C. To monitor tire pressure.
• D. To apply hydraulic or mechanical brakes to secure the aircraft on the ground and prevent unintended movement.

Answer: (D)

The parking brake’s job is to hold the aircraft in place on the ground by applying the wheel brakes, so the airplane cannot roll away when parked, during loading, fueling, or maintenance. It uses hydraulic pressure or a mechanical action to apply braking force to the main wheels and, in some designs, locks that braking pressure in place.

This is not about powering the landing gear extension, nor about releasing a landing gear lock, and it isn’t concerned with tire pressure monitoring—the parking brake is specifically for securing the aircraft on the ground by braking.