I've seen a few posts that go like this: 'I've played for a long time, but no new aircraft are avalible.'
If you play for a while and the planes aren't showing up, try this. It works all the time, every time.

• Open the CFS3 folder, and the campaigns subfolder. It should look like... C:\Program Files\Microsoft Games\Combat Flight Simulator 3\campaigns
• Make a copy of "fortress euorpa.xml" to your desktop if you screw up or want to change it back. Don't edit this one.
• Open "fortress europa.xml" with notepad. The one in the campaign folder, not the desktop.
• Right in the middle of this file is a list of aircraft and then a date. It's under the heading <TechTree>. Find it.
• Wherever it says <Date Month="3" Year="1945"/>, change that to, say... <Date Month="1" Year="1942"/>
• Overwrite the old file.
• Start a new campaign. All the aircraft are avalible. You're welcome.