The key to making a cake shaped like an airplane (or any object for that matter) is the structure of the base.
Here's an example that should guide you.
Here are some tips to remember:
- It's best to bake several cakes, so that you can cut out the right shapes and wedges required to make the airplane cake.
- The same goes for icing sheets etc... Roll out plenty, and plan which shapes and colors you will need before hand, so you can simply cut and assemble them when it comes to preparing the final cake.
You can also pick up custom designed icing for your cake from companies like http://www.ticings.com/