In PilotWings 64, there is one star for each level that enables your character to transform into the Birdman suit. We've already posted how to attain the first in Beginner Class. Here we list the rest. Each of these is best found with the Rocket Belt, because of its sharp maneuverability, and the ability to stop in mid-air, a feature you'll definitely need to attain a couple of these puppies.
The second star is in the center of Central Park, New York City, which is on the east side of the "island" in the Little States.
On Ever-Frost Island, this star is located inside a cave from which a waterfall appears. There are two waterfalls -- take the smaller one on the right and follow the cave until you've reached the end. Change your viewpoint to top down and you'll see an underground cavern. Lower yourself slowly down and it'll be there.
The fourth star is on Crescent Island and is located in a cave, along the ocean, between the airport and the little village, and is located inside the rock face.
In each case, once you've attainted the star, the screen will turn white and you will immediately begin again as birdman.