Mainline (aeronautics)

So, you know how planes have different parts, like the wings and the engines? And you know how they need fuel to fly? Well, the mainline is kind of like the big tube that carries the fuel from the tanks to the engines.

Think of it like a straw that you use to drink juice. The juice can't just magically go from the cup to your mouth, it needs the straw to help it get there. So the mainline is like the straw for the fuel.

The mainline is very important because without it, the engines wouldn't be able to get the fuel they need to work. And if the engines don't work, the plane can't fly! So the mainline is a crucial part of the plane, even though you can't see it from the outside.