In this simple-but-hopefully-fun game your mission is to fly Sonic through Badnik-filled skies in pursuit of Dr. Robotnik.
Kill 25 Badniks in each level to progress to the next one, until you reach level 4 for an aerial battle with Robotnik. Defeat him, and the game will loop back to the start but with faster flying Badniks each time through, until the game becomes extremely quick and challenging. See how many times you can play through the game to get the highest score you can.
Just like the controls in a real plane, use the Up arrow key to move Sonic's plane down, and the Down arrow to move the plane up. Use the Left arrow key to move left and the Right arrow to move right. Press the Space Bar to make Sonic jump (to kill the Badniks and attack Robotnik).
There is an invincibility cheat just in case you feel the need to use one - press Up, Down, Left, Right + "A" in the title screen to activate it - Sonic will turn yellow and will be invulnerable to enemy hits if you enter the cheat correctly. (But since you can then never die, you will need to either press your keyboard's F5 key or click your browser's refresh button to reload the game and reset it back to "normal" mode.)
I hope you enjoy playing!
Pete.