中文摘要：

地形感知与告警系统（TAWS）的目的是避免可控飞行撞地（CFIT）事故，提高航空安全。基于模式三的告警原理，对飞机发生掉高后的正常轨迹以及规避轨迹进行建模。在大量飞行事件中统计无告警事故率和告警事故率作为系统性能指标，并基于SOC曲线的掉高阈值包线生成方法获得模式三告警包线。仿真结果和实际使用包线一致，表明模型合理性和算法有效性。

英文摘要：

Terrain Awareness and Warning System （TAWS） is designed to prevent the Controlled Flight Into Terrain （CFIT） accidents and enhance the flight safety. Based on the alert principle of Mode 3, the models of nominal trajectories and avoidance trajectories were established for the aircraft losing altitude. Two statistical parameters of incident rate and un-alerting incident rate were accumulated for a large number of flight events to evaluate the performance of the thresholds. A method based on system operating characteristic （SOC） was presented to get the alert envelope for losing altitude. The simulation results are identical to the practical envelope, which show the correctness and effectiveness of our models.