To make sure that all players are involved in the story, not just the main player, we have a team of 4 pilots as the main characters of the game (think A-Team or Ninja Turtles :) ). Each pilot has a unique personality and is fully involved in the story.
If you play on your own, you can switch between the pilots and pick the character best suited for each mission, because they also have unique stats, e.g. one might be better at scout-missions, the other a better heavy bomber pilot;
If you play with friends, each picks one of the pilots; in any case, all four characters are always fully involved in the story.