Basically, we can switch between fuel sources. For example, if we were to have drop tanks, then we could switch to those and then switch to our main fuel systems. How this could work is that we assign an engine to a fuel source, maybe more than one if we were to have something like two wing tanks. It could be activated by the activation groups, or maybe a new set of buttons so we don't run out of commands. This would be useful since with this, drop tanks are drop tanks, and you have a new responsibility when flying. Also, we could simulate the "backup" fuel tanks some planes have.