To achieve the goal of independent innovation, the aircraft industry in China has increasingly realized that it is significant to implement the systems engineering approaches in the civil aircraft development process. Therefore, more and more companies are trying to adopt the Guidelines for the Development of Civil Aircraft and Systems (i.e., SAE ARP 4754A), which is recommended by international civil aircraft organizations (e.g., FAA, EASA) as a convincible approach for developing civil aircraft types that can meet airworthiness requirements. Since some basic concepts in the guidelines are still inexplicit, it is difficult for system engineers to explicitly understand the guidelines and to implement them in the aircraft development practice. Therefore, this paper has employed Scientific Philosophy and Design Science to analyze the shortcomings of some fundamental concepts in SAE ARP 4754A, and then proposes a new set of explicit concepts for systems engineering, including behavior, action, function, need and requirement. It is expected that it is easier for domestic engineers in the civil aircraft industry to understand the essence of the systems engineering approaches with such more explicit concepts, and to implement the approaches in the development of civil aircraft.