In many ways they are similar to the Marines equipped with jetpacks. The only difference is that they are brought into combat riding on the side-seats of Jet Fighters. They do engage targets of opportunity while being flown into their dedicated drop-zone. Once on the ground they fight while their drop-ships provide cover with gunfire and missiles.
Lost Legion Fighter Crew units are met for the first time during the Welcome to Helios mission. Later on, they are only encountered in Veins of Helios.