Rotation

i have this code :

onClipEvent(load){
up=0
down=0
thrust=2
drag=1
}
onClipEvent(enterFrame){
if(Key.isDown(Key.UP)){
up-=thrust
_y+=up
}
if(!Key.isDown(Key.UP)){
if(up<0){
up+=drag
_y+=up
}
}
if(Key.isDown(Key.RIGHT)){
_rotation+=5
}
if(Key.isDown(Key.LEFT)){
_rotation-=5
}
}

why does it rotate and not move in its direction ? does anyone know