As another device to help with shooting an airshow, once you have your super-long lens that gives you just 2-5 degrees of apparent view, hunting down a small airplane high in the sky can be a challenge, not to mention tracking them.
I looked for an found (then bought) a hot-shoe mount for a red-dot finder (also known as a reflex sight) to put on my own camera. I dabble in astronomy, so I already had two red-dot finders so it was easy to put one on the camera.
The advantage is that you can use the RDF as a heads-up display, allowing you to track the sky and your target quickly, letting you pan with ease.
I use it so that I can quickly see where my camera is pointed when it's craned up in the sky without having to crawl around and look through the eyepiece, possibly upsetting the balance of my tripod, etc.
Oh, yeah, you can get the device here: http://www.photosolve.com/main/product/xtendasight/index.html