@Bottiger probably knows exactly how the mechanic functions, but in my experience, you need to be airborne for at least 5-7 seconds before you can use it, then crouch and look down.
This is so that people can only use this mechanic as a counter to being floated, instead of, say, allowing Hales to perform "Bombing Runs" on our servers, continually super jumping and weighing down to absolutely decimate an area with weighdown explosion.