Which hydraulic systems must be powered when checking brake wear?

When checking brake wear on the CRJ550, it is essential to power System 2 and System 3 while having the parking brake set. System 2 is primarily responsible for the braking system, which includes the main hydraulic power required to operate the brakes effectively. System 3 is also involved in the brake system and is used for the anti-skid and autobrake systems, ensuring all components function correctly during the inspection.

By setting the parking brake, you ensure that the aircraft remains stationary while the systems are powered, allowing for an accurate assessment of brake wear without the risk of movement. This approach ensures that all aspects of the braking system are functioning as intended, providing a comprehensive check of brake condition.

Conversely, while both System 1 and 2 work together for normal aircraft operations, System 1 is primarily tasked with other systems like landing gear and flight controls. Therefore, powering System 2 and System 3 provides the necessary hydraulic support solely for brake inspection without introducing unnecessary static loads or complexities associated with the full operation of System 1.