Hello with the jet trooper, you really have to kill the enemies using the jet pack function. (In the vertical position air) (secondary obtention of the jet pack)
You have the key that allows you to do it, I play on ps4 and I finish them vertically. I do them in coop.
When you use the jetpack, if you look in the viewfinder (with L2), you will hover and keep yourself in the air while continuing to use a little fuel, you have to kill enemies like that
For me the three challenges of the jet trooper its finish in coop
