The mishnah in Shabbos (102a) states that if one throws an object on Shabbos, forgetting that it's Shabbos, and it never reaches its intended target, he is not liable. One of the examples given is an object which is burned before it lands.
What is the case? If it's on fire before he throws it, it should be a life-and-death situation for which one is not liable - even for intentionally breaking Shabbos, and certainly if he forgot that it was Shabbos.
If it was on fire after he let go of it, then still, what is the case? Regardless of if the fire was from someone who knew it was Shabbos, someone who didn't know it was Shabbos, a fire that was conveniently placed there, or a random cow that was running wild because it was on fire, if the object is extremely air resistant, there's no chance that it could have been thrown (you try throwing a flat sheet of paper). If the object is able to be thrown, from as far as I'm able to tell, assuming the objet is able to be burned, it will always hit the ground before it finishes burning.
So what is the case of the Mishnah where someone throws something and it's burned before it hits the ground?