Which hydraulic systems must be powered when checking brake wear?

• A. System 2 and 3 with parking brake set
• B. System 1 and 2 with parking brake set
• C. System 1 and 3 with parking brake set
• D. System 3 only with parking brake set

Answer: (A)

The test relies on having the brake system pressurized to read the wear indicators accurately. In this aircraft, the wheel brakes are powered by two independent hydraulic circuits. To perform a reliable brake wear check, both circuits that feed the brakes must be energized so the brakes can develop proper pressure and the wear indicators can be read cleanly. With the parking brake set, the wheels are held stationary, allowing a safe, stable reading of the wear without the wheels turning. Powering the two required hydraulic systems (the ones that actually drive the brake calipers) ensures you get a true indication of the brake wear. Using only the other system would not provide the necessary brake pressure for the wear reading, so the correct procedure is to have the other two systems energized while the parking brake is set.