When the parking brake is set and hydraulics are deactivated, which component maintains pressure in the #3 brake accumulator?

• A. Main hydraulic pump.
• B. Parking brake shutoff valve.
• C. Brake accumulator.
• D. Nosewheel steering unit.

Answer: (B)

The ability to hold brake pressure with the hydraulics off relies on isolating the brake circuit from leakage paths. The parking brake shutoff valve is designed to seal the line to the brake accumulators when the parking brake is set, so the fluid that’s already in the #3 brake accumulator remains trapped there. Since the main hydraulic pump isn’t running when hydraulics are deactivated, it can’t replenish or sustain pressure, so keeping the line isolated is what preserves the stored pressure. The brake accumulator itself stores pressure, but it needs that isolation to prevent bleed-off; the nosewheel steering unit has no role in maintaining brake accumulator pressure.