The technique is called a state space model [0]. A complete airplane might have been a bit hyperbolic, but as long as the assumption of linear dynamics is allowable, extremely large systems with multiple inputs and outputs and thousands of states can be simulated. What's more, there are some elegant and practical ways to find controllers with mathematically proven performance (like LQG control, or Model Predictive Control). This field of study has lead to the Kalman filter, which might ring a bell.

0: https://en.wikipedia.org/wiki/State_space_representation