How did the [Vomit Comet][1] maintain its free-fall trajectory?  Careful trimming?  Custom autopilot software?  Or just good stick and rudder technique?

Wikipedia, citing references but without substantiation, suggests manual control of at least the throttle. To use an automotive analogy, a trained pilot could correct for which direction the fuzzy dice are hanging from the rear view mirror, by playing the throttle and elevator and spoilers.  But even a legend like Bob Hoover might lose precision doing that dozens of times in a row.


  [1]: https://www.nasa.gov/vision/space/preparingtravel/kc135onfinal.html