How many hydraulic systems, and what are HYD 1/2 and HYD 3 roles?

• A. Three independent hydraulic systems: HYD 1, HYD 2, HYD 3; HYD 1 and HYD 2 primarily power primary flight controls; HYD 3 powers secondary surfaces and certain actuators
• B. Two systems; HYD 1/2 power primary flight controls; HYD 3 powers secondary surfaces
• C. Four independent hydraulic circuits; HYD 1/2 for landing gear; HYD 3 for brakes
• D. Three independent hydraulic systems; HYD 1 powers air conditioning; HYD 2 powers elevators; HYD 3 powers spoilers

Answer: (A)

Three independent hydraulic systems provide redundancy for flight control and other essential functions. HYD 1 and HYD 2 power the primary flight controls—ailerons, elevator, and rudder—so you maintain control authority even if one system is lost. HYD 3 powers secondary surfaces and certain actuators, such as spoilers and other non-primary control devices, ensuring those surfaces still operate when the primary systems are not available. The HYD 1/2 designation reflects that the primary controls can be driven by either HYD 1 or HYD 2, offering continued control as long as at least one of those systems remains pressurized. This separation enhances safety by not tying all critical surfaces to a single hydraulic source.