When the parking emergency brake handle is pulled, which component sets brake pressure?

When the parking emergency brake handle is pulled, which component sets brake pressure?

• A. The PTCU
• B. The hydraulic pump
• C. The emergency accumulator
• D. The main landing gear actuator

Answer: (A)

When you pull the parking emergency brake, the Parking/Brake Control Unit (PTCU) takes that input and sets the brake pressure. It acts as the braking system’s controller, translating the handle position into a target hydraulic pressure and then coordinating the hydraulic circuit to reach and hold that pressure in the wheel brake lines. The PTCU may draw on the hydraulic pump as the pressure source and, if needed, use the emergency accumulator to supply pressure, but it’s the PTCU that determines how much pressure is applied. The emergency accumulator simply stores pressure for use in certain situations; it doesn’t actively decide the brake pressure. The main landing gear actuator uses whatever hydraulic pressure the system provides to move or apply brakes, but it does not set the pressure itself.

When you pull the parking emergency brake, the Parking/Brake Control Unit (PTCU) takes that input and sets the brake pressure. It acts as the braking system’s controller, translating the handle position into a target hydraulic pressure and then coordinating the hydraulic circuit to reach and hold that pressure in the wheel brake lines. The PTCU may draw on the hydraulic pump as the pressure source and, if needed, use the emergency accumulator to supply pressure, but it’s the PTCU that determines how much pressure is applied. The emergency accumulator simply stores pressure for use in certain situations; it doesn’t actively decide the brake pressure. The main landing gear actuator uses whatever hydraulic pressure the system provides to move or apply brakes, but it does not set the pressure itself.