"In aircraft applications, biodiesel is used as a blend, rather than 100%. This is necessary in order to reduce the effects of biodiesel's low temperature crystallization and thickening. If you were in an airplane at 20,000 feet, where the temperature is possibly well below freezing, and your fuel thickens to the point where it can't be pumped to the engine, that's a very bad situation." I found that on another website.

I think in the future, biodiesel would have to have an aviation grade developed in order to run on 100% biodiesel. I guess piston driven aircraft normally wouldn't fly to such high altitudes and it is less of a concern than a high altitude aircraft. I actually read somewhere that to create a bio jetfuel, a blend of biodiesel and ethanol would create the cold temperature properties similar to jet-a