Maps & More:
At the "game select" screen, hold L+X and press Y.You'll hear a special sound effect upon entering this code correctly; now all of the planes, maps and missions will be unlocked.

GameShark Codes

Enable All Levels/Planes
4B4B4B25E06DF041
E070704100000000

Enable Level 30
CB3BF31400000001

Infinite Machine Guns In Tactical Mode
A0F345BD00000200
55AF637B00000200

Score 100 In Tests
2217747C00000064

Unlock F-15DJ Aggressor 2
9EA80CA00000001

Unlock XF-3 Super Recipro Fighter
5747711A00000001

Thanks to Revolution readers andrew and Joseph Tuvera!