Answer
$720$
Work Step by Step
We know that if we want to select $r$ objects out of $n$ regarding the order, we can do this in $_nP_r=\frac{n!}{(n-r)!}$ ways.
The first plane leaving is determined by the number of passengers, the other $6$ are "random" in terms of order.
Hence here the number of possibilities is $_6P_6=\frac{6!}{(6-6)!}=6!=720$
