I have no problems downloading the planes and installing them but when I want to fly them, they are not available. I have downloaded 12 planes and am only able to find and fly 4 of them.
Where did they go?
Are you sure that you are taking the right file out of the zip file and putting into the right FSX folder. Also if the planes are for FS9 they might not work or if they have an installer thats not for FSX.
They could also be listed under a name that you didn't think they would be.
Look at all the categories in your menu.
Some planes has the folder in another folder, like the continental 737-522 on page 12 on the FS2004 download jets catagory. It's real plane folder is inside another folder. You can reconize the real plane's folder by looking in it. It has the aircraft.cfg, model folder, texture folder, etc. If you put the outer folder in Flight Simulator will not reconize, you are suppose to put the folder that CONTAINS aircraft.cfg, texture, panel, model,etc. Other cases are the plane is texture only. If you use FSX, many of the 737-800 are texture only!