As the Alien in level 3, the Queen will tell you to get to the bottom of a 
shaft with a giant fan at the top. As you get close to it, another Xenomorph
will be swept away and blown into the fan. If you use your Focus, you can see
two vents on the opposite wall. Choose either of them and you can safely jump
to it despite the power of the fan. As you go, you will find more vents to hide
in. Use them to make your way down.