Which statement is correct regarding hydraulic systems in aircraft?

Hydraulic systems in aircraft are essential for their ability to efficiently transmit power to various components, particularly for moving control surfaces. This is done through the use of hydraulic fluid, which is pressurized and directed to actuators that control the ailerons, elevators, and rudder, as well as other mechanisms such as landing gear and brakes. The use of hydraulics in aircraft enhances response times and allows for precise control, making it an important feature in both civilian and military aviation.

The other statements do not accurately describe the function or application of hydraulic systems. They are not primarily used for electrical power generation; that role is typically fulfilled by generators and alternators. While some systems may use air pressure in conjunction with hydraulic systems, they do not operate exclusively on air pressure; they rely on hydraulic fluid mechanics. Lastly, hydraulic systems are widely used in both civilian and military aircraft, making any claim that they are limited to civilian applications incorrect.