I mostly use P or Av Mode. Single Frame Shooting for static aircraft, on pushback or taxiing, and continuous shooting for approaching shots or aircraft gaining speed and rotating...
Usually ISO 100.
Slightly off topic, but what exactly is the difference between P mode and automatic? Is it only that in P, you can change ISO? I usually shoot in Av or Tv, depending on conditions, and always try to stick to ISO 100. When using Tv, I try to set the time fast enough not to get blur, but still slow enough for a good aperture value (around 8).
I guess that's what happens in the end, you start thinking about the beginning.
'P' doesn't use flash automatically. It just gives you a combination of shutterspeed and aperture. The 'little green square'-automatic mode pops out the flash automatically when it gets too dark... Not sure if it also messes witht the ISO...