Finish the game and see the Normal or Bonus Ending. A new option will appear after you picked the difficulty under the "START GAME" option at the Title Screen. Using this option, you may have a chance to buy some new aircraft as you play through the game again.
Free Mission Mode:
Using the "EXTRA" Aircraft Mode, finish the game and see the Normal or Bonus Ending. After the "START GAME" option at the Title Screen, the "FREE MISSION" option will appear. Now, you can play all the missions you have discovered so far.
The Normal Ending:
Play the game up to the 19th mission, "Kingpin". Finish the mission withoug shooting down pilot Z.O.E. (The enemy plane that is marked as 'DANGER' in the Briefing Screen.)
The Bad Ending :
On the 19th mission, shoot down the pilot name Z.O.E. You can then play the 20th mission. If you don't shoot down the cruise mission in this mission you will then see the Bad Ending.
The Bonus Ending:
On the 20th mission, "Last Resort", be sure to shoot down the cruise missile. You will then be able to play the 21st mission, "Fighter's Honor". Finish this mission to see this "Bonus Ending".
Play the game and achieve a rank higher than First Lieutenant. A new option will then appear in the Options Menu. Inside, you may play all 28 music tracks from the game!