Whether it is an Air Force or a civil aviation organization, flight safety in reducing the accident rate has always been the most crucial goal of every aviation organization. The purpose of aircraft accident investigations is to identify probable causes and related risk factors and provide safety recommendations to prevent the accident from happening again. Although human factors have always been the major probable causes of aircraft crashes, the conclusions of those investigations, according to the cheese model, are just because the flight crews were only the last defensive net to produce unsafe behaviors leading to the accident.

　　It is always a challenge for investigators to identify the actual causes of an aircraft accident, particularly human factors; therefore, selecting a proper investigating method is essential. Professional, theoretical, and updated investigative tools help correctly confirm the incident's cause, especially involving human errors. The study utilizes the "Human Factors Analysis and Classification System (HFACS)" to analyze four Control Yuan's R.O.C. Air Force (ROCAF) accidental reports. Results prove that every higher level in the HFACS directly affects the lower level, and the human factors, from the highest level of organizational management to the lowest level of pilots' operational behavior, are closely related. That relationship is far more complicated than just contributing to pilots' errors.