同学你好，该知识点来自沪江网校《新概念英语1、2、3、4册连读【特惠班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学你好~
while we were waiting to land是while引导的时间状语从句

a flight attendant told us to keep calm and to get off the plane quietly是主句
其中a flight attendant是主语
told是谓语
us 宾语
to keep calm and to get off the plane quietly 是宾语补足语

as soon as it had touched down是as soon as引导的时间状语从句

完成时也可以在until, as soon as等引导的时间状语从句中表示将来。
I’ll wait until he has written his letter. 我愿等到他把信写完。

这里就是在过去时间框架下，用过去完成时，表示过去将来完成了着陆后，人们就下飞机。

祝同学学习进步~