Traveling guitar player unite......................and help me?

ok so i know you have to loosen the strings when flying but how much. it is a fender strat in a coffin case with dr dimebag light top heavy bottom strings(10-42) so tell me in steps, you know half step full step, or tell me how much to turn the tuning heads. it is i think droped d or low c but i'm putting it on standard right now.