Excellent beginning, flyhigh!
One of my first suggestions is to learn how to use your camera without all of the nifty automatic features. Knowing how the camera works before allowing it to make decisions for you is a must if you want to walk away with first class images. For instance, you used autofocus, right? That pesky computer in your camera thought the fence was the most important part of the image, so it focused on that instead of the plane. If you had done the job on your own, you could have tweaked the focus to throw the fence out of focus and sharpen up the subject a little more.
You're also using the autoexposure feature and it's being fooled by a tricky situation. The camera meter thinks like Iain - it wants you to shoot with the sun directly behind you. Unfortunately, that often makes for rather flat lighting. If you can incorporate shadows to emphasize the shape and contour of the subject, you'll have a much more successful image. The hard part is getting the camera to give you the proper exposure. In this case, the images came out a little dark. What happened is the meter saw the bright, sun-lit blue sky and said to itself, "Wow! That's way too bright! I'd better make it darker so that it looks like a middle tone (or brightness)." The result is that your sky, your planes, and your fences all look just a smidge too dingy and dark. Ever see a photo of snow that looks like ash? Same thing happens there, too. The converse is that you can photograph something dark (like a crow or an SR-71) and the camera will try to make it lighter.
The solution, as with the autofocus, is to take control of the automation. Tell the camera what you want to properly expose or just do it all yourself. Unfortunately, without knowing what kind of camera you use and what your photographic background is, there are too many possible methods to explain here. Get out your manual and see what it says about "exposure compensation." That will give you a good head start and let you boss that camera meter around a bit more.
As for your composition, you could, indeed, tighten up the framing a bit. However, remember that a tight shot isn't automatically a good one. Give the subject room to live; Think about the story it's trying to tell. If a plane is landing, we know that it's descending and moving forward . . . give it room to do the same in the image. Compose the photograph with the plane slightly higher than the middle of the frame with space for it to move into. You might even be able to include the runway in the bottom of the image so that the story is more complete and we know what the ending will be. The same applies to the horizontal framing. Give the plane room to move forward and into the story. Play with the composition of different planes and phases of flight and find the storys that say the most to you.
Now, on that note, let's talk about subjects that are dead center in the frame: Why do most average photographers stick the airplanes in the middle? First, they often don't think of the flow, composition, or story. Second, they use autofocus and . . . the autofocus sensor is where? In the middle of the frame! Can you imagine what Ansel Adams' images would have looked like if he had been forced to put every subject in the center of his frame because he was a slave to his autofocus sensor? Yuck! Yet another reason to go manual before you embrace the technology that your camera unfortunately came with.
Check your local Community Ed programs for some basic black and white photography classes. They're a great way to learn about how cameras work and how to make them work for you. Good luck and keep it up!
