If a series of defective components causes the available hydraulic pressure to decrease to 0, how can the rudder be controlled?

The rudder can be controlled through cables by mechanical input only when the hydraulic pressure is lost, such as when it reaches zero due to a series of defective components. This mechanical system operates independently of the hydraulic system and allows for direct physical control over the rudder's position.

In aircraft design, control surfaces like the rudder often incorporate secondary systems, such as cables and pulleys, which can be used in the event of a hydraulic failure. By relying on a mechanical system, pilots can maintain control of the aircraft even when the primary hydraulic system ceases to function.

The other options involve methods that are either not functional during a hydraulic failure or are dependent on external systems or approvals that would not provide immediate control of the rudder.