# Security Situation Assessment for Terminal Area Control System Operation Based on BN-ISSA-ELM
## 2 Materials and Methods
### Construction of the Operational Safety Situation Indicator System
The Cronbach's alpha coefficient value of the first part of the questionnaire on the agreement of the factors influencing the operational safety posture of the terminal area control system is 0.897, and the [PERSON]'s alpha coefficient value of the second part of the questionnaire is 0.871, which indicates that the reliability of the questionnaire scales is very good, and that they can be used for the assessment of the operational safety situation of the terminal area control system. The 19 secondary indicators identified in this paper are as follows: personnel technical level, personnel cooperation, personnel safety awareness and responsibility, personnel working procedures, personnel physiological condition, personnel psychological condition, personnel deployment, equipment reliability, equipment deployment, equipment loading, control agreement system, safety training management, scheduling, radio interference, air traffic congestion, adverse weather conditions in the airspace, the reasonable design of flight procedures, military aviation activities, and bird strikes. Based on the categorization of human-aircraft-environment-management, examples of the impact of each of the secondary indicators on three typical unsafe events are presented below. Figure 3: Security situation indicator system for terminal area control system operation. Personnel with a low level of operational skill may give inaccurate altitude instructions when directing an aircraft to climb or descend due to insufficient knowledge of the aircraft performance, airspace structure, and altitude layer allocation rules, resulting in the aircraft deviating from the intended altitude. A lack of ability to handle the details of approach procedures and various special situations may prevent the pilot from being provided with a reasonable descent profile guidance, making it difficult for the pilot to maintain a stable rate of descent, speed, and heading during the approach process, which may lead to an unstable approach. The inability to accurately calculate the interval between airplanes due to insufficient operational capability may result in the issuance of incorrect heading and speed instructions, making the distance between airplanes too close and triggering a dangerous approach. Poor cooperation between controllers and between controllers and pilots, or the inaccurate or untimely transmission of information, may lead to misunderstanding or the delayed execution of instructions. Personnel with a low safety awareness may be paralyzed in their work, may not strictly follow the standard operating procedures for assigning altitude layers, may not monitor the altitude of the aircraft well, may fail to detect and correct the altitude deviation of the aircraft in time, and may ignore the potential safety risks, which may lead to the occurrence of unsafe events. The ineffective implementation of air traffic control and collision avoidance work procedures, whether by controllers or pilots, can increase the probability of risk occurrence. The physiological conditions of the personnel, such as the level of fatigue, may make them negligent in their work, causing unsafe events to occur. Controllers may also suffer from command failures when they are under excessive work pressure, emotional stress, or anxiety, and so may be less sensitive to air traffic conflicts, thereby failing to detect the signs of approaching hazards in a timely manner. Equipment reliability problems may result in untimely or inaccurate information updates, so personnel may not be able to accurately determine the actual spacing between aircrafts and to effectively prevent hazards from occurring. In some small airports or remote airports, poorly equipped equipment, such as the absence of an ILS or its low accuracy, may make it difficult for personnel to ensure a stable approach. When the equipment is overloaded, the performance will decline, increasing the probability of unsafe events.