I would suggest you actually start by reading the online help on some basics and watch some tutorials. There is nothing disappearing, your layer is simply larger than the actual composition and AE does not display content outside that box. You will simply have to work in a larger (pre-)composition for your flight path animation and then do the zoom in/ scaling in a second step in a parent comp sized to the final output dimensions. These are basic workflow things. Again, please read the help or watch some tutorials.
Mylenium