I'm still very new to flying a Tarot PRO Hexacopter and APM 3.2.1 and its been fine up to now, I have about 4 hours of flying experience with out incident. I added my FPV components and was about 11 minutes into a perfect flight in Loiter mode and low wind and good weather conditions. While hovering my machine at approx 30 meters altitude it suddenly started a shallow Toilet Bowel effect and got progressive more severe, and then also lost complete control. I tried to activate RTL with no effect. I then switched to Stabilize but because I had pulled the throttle to zero for RTL my machine inverted and was heading for the ground at a rapid rate. After applying full throttle I saved my machine from complete destruction with about half a meter above ground level.
My question is what causes Toilet Bowel effect and what should I do to fix it. Can antbody help please.