Shot 1:
DSC01530 on Flickr - Photo Sharing!
ISO 400
Aperture f16
flash used
Ok righ there we have your first problem - your aperture - its way too small.
shot 2
DSC01484 on Flickr - Photo Sharing!
ISO 800
Aperture f29
shot 3
DSC01496 on Flickr - Photo Sharing!
ISO 800
Aperture f45
Ok notice how your shots are getting softer and softer and your aperture is going up and up (or rather down and down as the smaller the aperture the bigger the f number). Around f16 diffraction starts to take place and will lead to you getting softer images - way out at f45 and its a major problem! I shoot a lot of macro where depth of field is very small and even I don't go much below f13 most of the time and f16 is my lowest limit.
Also the higher you take your ISO the more noise your going to get in your shots - that means even more softness to details.
But your in good lighting so you should not need a high ISO to get that fast shutter speed. Also your aperture is way too small for this sort of work really - sure its nice to have, but at the range the planes are flying at you should not really need to be going above f8 (I would guess).
So cut your aperture right back to say f5.6, and your ISO down as low as you can whilst retaining a good shutter speed. Those two things together should help you get a far improved quality of image to work with.
And honestly I do like what I see in all 3 shots - good focus and good composition (I think) just marred by the softness your getting.
Also the small apertures you have used have shown up spots on your shots (the big ones) which is dust on your camera sensor - it should not be a problem when shooting wider at say f5.6, but it is something to look into dealing with at any rate - so do a readup on camera sensor cleaning.
EDIT
I would also strongly recomend you get hold of a copy and read "Understanding Exposure" by Bryan Peterson - it will help you understand aperture, ISO and shutter speed with more depth than can be relayed in a forum post (Because you can write a book on that yah know

)
Also take a look at this website here:
Ron Bigelow Articles
And get a readup on: Levels, curves, depth of field, histogram, layers, noise, shadow/highlight detail, sharpening, threshold
That should give you some good grounding in editing shots - note that even if you don't have full photoshop this lot all applies - photoshop elements is a weaker version but can do most of it and there is a range of 3rdparty downloads you can get (free) which expand on its functionality