Bakedbean, . .. .I'm just curious why you believe that a cold aircraft has less potential energy at a given height than a warm one? Potential energy has nothing to do with temperature (at least in this instance). Potential energy is a function of mass, gravity and height. I could be wrong as I am not a physisist, but from what I've learned in physics classes, I think I am right. There may be more complex formulas that provide a better model of potential energy, but I seriously doubt that temperature would be included in it.. .. .E_p = mass * gravity * height