When i fly in the air with the regular mode, then fall down and slow myself down before i hit the ground so i fly a bit (1block) up again so my falldamage should be nothing, but when i hit the ground i take 5 to 7 hearts of damage.

that's not a bug its from the minecraft files its because you keep getting up then down because its in regular mode so it counts every up and down so if you kept going up and down for 100 times you would get 100 hp of damage
But that's fixed in 1.10.2 for me

Ok that explains why i´m taking so much damage but isn´t it still a bug that the jetpack doesn´t reset the falldamage, or maybe its a problem with another mod if it doesnt happen to you.

I think I experienced some issues with high damage amounts from jetpacks in 1.10.2 too, but strangely enough I think that was when going upwards to land on something? I might be misremembering as I haven't reproduced it since.

Note that I crafted Free Runners soon after to negate fall damage.

Going up and landing on something hurts me as well

just use the free runners it will stop fall damage

True but its still a bug

Not yet, i´ll do that and check if it still happen when i´m playing next time

did you update to 9.2.1

Running Mekanism-1.10.2-9.2.1.298 and this issue is still here. I think this should be adressed as soon as possible. The free runners work but this is still quite a bug o.O