after 用法讨论!three years after his flight over the North Pole.

after 用法讨论!
three years after his flight over the North Pole.此句中 three years 可不可以放在after 后面,这是不是after 的一种特殊用法,
此在句完整是three years after his fight over the Norht pole ,Mr.Byrd successfully flew over the South Pole for the first time .
那么我们该如何理解over呢,它是作动作还是介词.
如果去掉three years after .his fight over the North Pole应该可以作为一个完整句子.我们该如何理解 after