How are pneumatic systems distributed in an aircraft?

Pneumatic systems in an aircraft are typically critical for the operation of various functions such as environmental control, engine starting, and systems actuation. The correct answer reflects the interconnected nature of these systems.

Using interconnected crossfeed ductings allows for flexibility in distributing pneumatic pressure throughout the aircraft. This design enables multiple systems to share the same pneumatic source, facilitating redundancy and optimizing the use of available resources. If one area of the system experiences a failure, the interconnected nature allows other areas to still function, enhancing overall reliability and safety.

The other options suggest more limited or isolated configurations, which do not accurately represent the typical design of pneumatic systems in aircraft. Separate isolated systems could lead to inefficiencies and increased complexity. A single main line would not provide the necessary redundancy and could create a critical failure point. Relying solely on individual valves would not support the diverse and demanding operational requirements of an aircraft's various pneumatic needs.