I agree with Number 5 above, where in my teens I was afraid of flying, though it neve kept me off the planes, since I hadn't much choice with my family living in Singapore, and still going to school in the states.
Not knowing HOW the plane stayed up really bothered me, along with how it stayed up despite BAD turbulence. I recall one time flying LAX
in business on a red-eye, and it was so bad no one was able to sleep, and the window shades were up at this point, and while I focused on the seatback in front of me, in my periphery, I could see the cloud deck below out of both eyes and how much it was moving up and down thanks to the turbulence. So my fear then was how does this plane not roll over if it is rolling side to side so much!
And a small part was putting my life in someone elses hand entirely, which as a control freak, was kind of difficult combined with a fear of heights.
But now in my early 20's I can say I have put to rest all of my fears of flying after a few physics courses.