A bound spirit is wired into the piloting system of the vehicle, allowing it to make a simple Maintain Control action each Combat Round without the pilot needing to spend an action or even be present.
The pilot can communicate (albeit one-sidedly) with the soul pilot to make their wishes known, but the soul pilot makes the decisions for how to spend its actions making training the soul pilot an important part of the construction process. Souls are known to be erratic at times and can learn unintended lessons, but can also be extremely useful.