What are the major hydraulic systems on a typical airliner and which primary systems/components are powered by hydraulics?

• A. Typically multiple independent hydraulic systems powering flight controls, landing gear, brakes, thrust reversers, and some flap/slat actuators.
• B. Only landing gear.
• C. Only flight controls.
• D. Only cabin pressurization.

Answer: (A)

Hydraulic power is used on airliners because it delivers a lot of force in a compact, controllable package, which is essential for moving large control surfaces and gear quickly and reliably. Because safety depends on staying controllable even if part of the system fails, aircrafts design multiple independent hydraulic circuits so a failure in one circuit doesn’t leave critical systems without power.

In a typical airliner, you’ll have several hydraulic systems, and each one powers a cluster of major components. The primary ones are the flight control actuators (for ailerons, elevators, rudder, and often trim surfaces), the landing gear extension and retraction mechanisms (and door actuators), the wheel braking system (including anti-skid components), the thrust reversers, and several flap/slat actuators. Some aircraft also use hydraulics for other surface actuation, but these are the core areas that rely on hydraulic power for normal operation.

Power for these circuits comes from engine-driven hydraulic pumps, with additional pumps driven by the APU or electric sources to provide backup or ground power, and accumulators to store energy for rapid actuation. This combination gives high power, precise control, and redundancy for essential systems. Note that cabin pressurization is not hydraulic; it relies on a pneumatic/bleed-air/environmental control system.