General comment: All these files are too small, i.e. they have already been compressed, which will increase grain.
VN80.jpg : Camera is not level. Rotate the picture about 2 degrees to the right. Apply a little bit of sharpening, but be careful not to do too much - there is grain starting to show up, especially around the engine. That grain might actually be scanner noise - does your scanner support multiple passes? That might help. Beware of taking pictures when the sky is hazy-white like it is here. It really makes the easthetics of the picture suffer. The toughest part to fix will be the fuzziness around the edges of the verticle stabilizer. You might consider rescanning at a very large size, and downsizing it using an anti-alias algorithm, if your software has it, before sharpening up. Finaly, a little color saturation would help.
USX1900D.jpg : This one is pretty blury, but already quite grainy. You will definately need a better scan - a file which is both grainy and blury like this is beyond repair I'm afraid, as reducing the blur will make the grain even worse.
737.jpg : Similar problem as USX1900D.jpg above, though not as bad. A new scan would also be in order, I think. Use masks to allow you to sharpen up the plane without affecting the sky.
CO739-2.jpg : Needs to be rotated 2 or 3 degrees to the right. Needs a new uncompressed scan, as it is already quite grainy. Lighting here really washed out the dynamics of the colors - a little saturation would be in order.
SW737-2.jpg : Too much compression, grainy and very dark. Definately needs a new scan. I don't mind having part of the plane cut off - the angle is interesting, but the fact that you cannot see anything in the shadows ruins it. I managed to improve it a lot by really pushing the gamma hard - the bottom of the plane, landing gear etc became very clear without overpowering the bright areas, unfortunately the scan quality could not handle the gamma increase without a lot of horizontal and vericle banding.
Falcon900.jpg : Needs a lot of sharpening, and needs to be a bit brighter. Try to mask the sky so that you don't sharpen it as well.
AF340.jpg : Not bad, although damaged by already being too compressed. On a new scan, make it a little bit sharper (not the sky), and a little color stauration as well.
CO739.jpg : Nosegear got cut off. Recrop to include it, and some careful sharpening, and it has a chance (although I would try with a new, uncompressed scan.)
CO735.jpg : Exactly the same as CO739.jpg, although the nosewheel is now visible
. In addition, I would brop out the left side of the picture to center more on the 737.
Connie and KC.jpg : A little more sharpening and saturation could be useful. Level off the ground as well
The lighting was not very good for this kind of shot, but you had a good idea.
KLM747.jpg : Probably too far gone to be saved. Motion blur on everything, including the aircraft.
I hope that helps.