Good points on the panning. I didn't think of mentioning that when I said to pre-focus on the spot you plan to shoot the airplane at. it just comes so naturally I didn't think to clarify.
I think that most people start by trying to just wait for the airplane to fly into the frame, then hit the shutter, but that's going to put the yield down to about 1%! You can tell that when they start talking about really fast shutter speeds to "freeze" the airplane. You can get focal-plane shutters that go as fast as "1/8000th" of a second but that's still not enough and would only yield massive distortion - since it really work at 1/8000th of a second, it's more like 250th of a second but moves both curtains at once to form a narrow slit that scans across (usually from bottom to top).
The key takeaway is that there really isn't any particular magic about doing these pictures, learn the equipment you have and use the right (relatively simple) technique. The rest of it is like any other photography, fill the frame to the extent possible, focus on the interesting part and exclude the rest somehow, practice and experiment, and get a big SD card.
BTW - what is your yield? I mean technical yield (in focus, not unintentionally blurred, no airplanes or head cut off, salvagable exposure) rather then artistic/photographic yield. On the former I just checked a few folders of airplane contest pictures and I was doing better than I thought, maybe 75% were technically acceptable (to me) and about 25% were actually good pictures. I spent a lot of time using film cameras and in particular, large format, so I am not that profligate when pushing the button, but 75% was higher than I would have guessed.
Brett