It would reduce the plane's weight by a trivial amount, like eating ice cubes to lose weight (nutritional "calories" = 1000x heat calories). Also, helium requi

It would reduce the plane's weight by a trivial amount, like eating ice cubes to lose weight (nutritional "calories" = 1000x heat calories). Also, helium requires airtight containment - which itself would add weight. Not belittling you; trying to explain the problem better for you.