In the system of traffic alert and collision avoidance system (TCAS), the time of closest point of approach of the aircraft, horizontal miss distance (HMD), and vertical miss distance (VMD) are the primary parameters to describe the concept of collision avoidance.
在TCAS系统中,到达最接近点的时间Tau、HMD和VMD是描述空中碰撞物理过程的主要参数,利用该组参数能够完整地描述TCAS系统的防撞机制。