I cant use turn off an entities gravity when it touches the ground

I'm trying to make a a flying/land entity by making it so when it jumps it has no gravity and flys and when it touches the ground it gains back its gravity but for some reason it doesn't use this specific piece of code (is Event/target entity on ground) is this just some weird bug or do I just not understand something?

EDIT: for some reason it only doesn't work with gravity everything else (that I know of) works fine