To keep the story short and simple, I collected my 450QS from the shop and took it for hover training. All was ok until the tail servo suddenly stopped working. The heli yawed uncontrollably and plunged into the ground. Luckily, minimal damage was done. I called the shop who fixed the heli initially....

The ball link was loose when screwed into the stock plastic tail pitch assembly on my KDS 450QS. Even after applying CA then screwing the ball link in, the ball link "disappears" before the helicopter lifts off the ground. Good thing I discovered it before I began with my hovering training exercise!...