When developing a new air traffic control system, the functional tests should be based on the needs and requirements of the end-users who interact with the system on a daily basis. Current air traffic controllers are the most critical stakeholders for eliciting criteria for functional tests due to the following reasons:

User Experience: Air traffic controllers have firsthand experience with the operational aspects and practical challenges of the system, providing valuable insights into functional requirements.

Operational Knowledge: They understand the necessary functionalities, safety features, and usability aspects that the new system must support.

Critical Feedback: Their feedback is crucial for identifying essential functionalities, ensuring the system meets real-world requirements and safety standards.