> They fly the plane downward, matching the vertical acceleration with the acceleration caused by gravity
"Contrary to popular misconception, the 0 g freefall phase of flight begins as the aircraft climbs, and does not occur solely as the aircraft descends. Although the aircraft has upward velocity during the initial 0 g phase, its acceleration is downward: the upward velocity is decreasing" [1].
Good clarification, thanks. By "downward", I meant downward acceleration, not necessarily downward velocity, although colloquial usage of "downward" usually means velocity.
"Contrary to popular misconception, the 0 g freefall phase of flight begins as the aircraft climbs, and does not occur solely as the aircraft descends. Although the aircraft has upward velocity during the initial 0 g phase, its acceleration is downward: the upward velocity is decreasing" [1].
[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2598414/