Here is my 100% Achievement guide and full walkthrough so you don't miss a thing.
The first time we get to fly our Saucer is in level 2 as we have to destroy buildings.
Pick up any object (car for max damage effect) with the
, line it up against a building or anything.
You can also aim if it makes it easier for you with
Then just let go and watch the achievement unlock and flyyyyy.
Go to 21:00 in my part 1 video to see where and how to unlock this
Hope this helps!