@ rokemon101: if you touch the green gas, even for a tiny amount of time, it'll still damage your plane slightly. you can tell if your plane has been hit by gas by seeing if your plane's guns are jammed or not. I had that problem too, thinking that I had beat the level untouched.
 "Pinata Hunter"){kind=icon}
 "400 Years"){kind=icon}
 "SteamBirds"){kind=icon}
 "Globetrotter XL"){kind=icon}
 "Battle Dawn"){kind=icon}