1）新概念2第79课：

I used to travel by air a great deal when I was a boy. My parents used to live in South America and I used to fly there from Europe in the holidays. A flight attendant would take charge of me and I never had an unpleasant experience. I am used to traveling by air and only on one occasion have I ever felt frightened.

2）新概念3第2课：

The big clock which used to strike the hours day and night was damaged many years ago and has been silent ever since.

书上都说：used to 表示过去习惯做某事，但强调暗示现在不做了！那么，请看新概念2第79课的句子，I used to travel by air...为何后面又说I am used to traveling by air...？很奇怪，以前习惯坐飞机...（强调暗示现在不坐飞机了），

为何后面又说我现在习惯坐飞机呢？

顺便请教老师，以上2句中的used to 是否都可以换用would呢？即I would travel by air a great deal when I was a boy...和The big clock which would strike the hours day and night...呢？