This is a Flash version of part of the Sky Chase Zone from the classic 1992 game "Sonic the Hedgehog 2".
Your mission is to help Sonic to kill 25 Valkyn badniks in each level in order to progress to the next one, and finally to take on Dr. Robotnik in an aerial battle. Use the Cursor keys (Arrow keys) to fly Tails's Tornado airplane towards the enemies and then use the Space Bar to make Sonic spin-jump off the wing to attack.
Be VERY careful though, because in this game the controls are reversed and are the same as in a real airplane!! You have to press the Down Arrow key to go UP, and the Up Arrow key to go DOWN!
There are twice as many badniks to kill in each level as in the previous one, and each time you defeat Dr. Robotnik in Level 4 the game returns to Level 1 and the badniks speed up.
Because the game becomes very difficult after a while, there is an invincibility cheat just in case you want 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.)