Ace Combat Zero: The Belkan War

It sounds like the aircraft you are missing are the F-2A and the F-117A. The F-2A is unlocked by completing mission 08B. The F-117A is unlocked by completing mission 14B. For each of these this should happen the first time you complete the corresponding mission, which will always occur during a campaign. These aircraft can be unlocked from any difficulty.

It is fairly rare in ACZ, but once in a while there are reports of players who are not able to unlock various items even though they have met the criteria. This is generally because they used restart/retry somewhere along the way. Not everyone accepts this explanation, but there are no credible reports of saved game corruption when restart/retry have been completely avoided, the PS2 and game disc are in good condition, and power to the PS2 is stable during all saves.

If you have completed these missions and do not have the corresponding aircraft, you can try completing the missions again in a campaign. They might unlock eventually. However, if the problem is persistent, you might have to consider whether or not you want to start over. If you do, you will need to delete your saved game file (or use another memory card), and then avoid ever using restart/retry. When necessary, quit and reload instead. Also, make sure your PS2 and game disc are in good condition, and that power is never interrupted during a save.