With those three systems, you have what is always necessary -- a level of redundancy that says, if one system fails, you'll still have a way to make sure that you're being controlled.
用这3套系统， 你就有了空中交通所必须的 某种程度上的冗余度 就是说，如果一套系统失效，你还有其他系统 来保证你的飞天车得到控制