Like this: crouch first, then jump while crouching. You could also use a keybind to use the jetpack with just one key on your keyboard. Add this lines into your steamapps\\common\\Half-Life\\valve\\autoexec.cfg . It will allow you to use the long jump by pressing “space”. //jetpack / longjump alias
alias "+lj" "+duck;wait;+jump"
alias "-lj" "-jump;wait;-duck"
bind "space" "+lj"