Conceptual design of aircraft tailored for a specific role requires a holistic view to account for requirements atdifferent levels, from systems to sub-systems and their components. This is the case with aircraft designedfor firefighting, where they collaborate and communicate with other systems towards a common goal. Thiscollaborative and holistic perspective is what a System of System (SoS) analysis tries to achieve. To conduct aSoS analysis, the use of Agent-Based Modelling and Simulations (ABMSs) is widely adopted. A crucial aspectof this approach is the ability to capture emergent behaviours that arise from collaborative systems, whichare represented in the Agent-Based Simulation (ABS) by agents whose actions are traditionally governed bydecision trees. The present study introduces a novel methodology using ABMS where a Large Language Model(LLM) plays the role of a human in the loop. The purpose is to represent the decision-making of an IncidentCommander (IC) by allowing a LLM to play this role within a wildfire situation. The IC will follow operationalguidelines and guide the agents’ behaviour in order to provide them with more degrees of freedom and removethe constraints associated with traditional behaviour trees. This approach not only aids in simulating realisticoperational scenarios but also generates valuable insights for Aircraft Conceptual Design (ACD), enabling thederivation of specific design requirements based on simulation outcomes.