GPX file Interpretation

Whoa, I bet that was scary.
I took a quick look at the GPX file, and 3 things jumped out.
1) at the beginning, you have an error indicating that the compass is disturbed by magnetic fields
2) at line 259, PH or AH seem to have lowered the power quite a bit (not sure why)
3) at line 274 of the file, it looks like the motor currents jumped really high (was this where you tried to recover?)
Flying with PH when your compass is unreliable is super dangerous. There are a lot of reasons why this can happen, including bad calibration, interference on the copter from something like LiPo wires, or interference from environmental factors.
Hope this is helpful...

 

It looks like you initiated an autopilot commanded decent not sure that was intentional or not. Line 258 shows a vario trim down. Before the descent on line 257 your hover current was at 92.4A then went up a bit to 95.5A then dow to 64A Then once you disengaged the AH your aircraft current dropped to 54 A then a slight increase in the next few lines. Then you went to max throttle and had the a current pull of 186A which is impressive because that's the highest I have seen it do.​

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My buest guess is that you stalled the rotors. I have entire explanation here.​

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A small rotor stall called "Vortex Ring State," is where the propeller is flying back into its thrust. This causes a disruption of the smooth air flow through propeller. If caught early the only part of the prop that is stalling is the area near the center hub. At this point you can throttle out of it you still enough lift in the rest of the prop. If caught too late and no corrective input is added then it gets exponentially worse the descent increases and more of the prop surface area gets disrupted and eventually will lead to the entire prop being stalled. This has caused a few more catastrophic mishaps on this forum where the pilot is bringing down and suddenly it drops aggressively out of the sky and hits the ground at a high vertical rate.​

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By looking at your hover gas values you were flying a pretty sizable mass. This effect gets worse the heavier the copter is. The strange movements are probably do to the auptopilots inability to compensate for stalled rotors because the thrust is no longer continuous. This stall can happen without a moments notice. When you see it the best reaction is to increase power as quick as possible and try to fly out of it preferably into the head wind. Lucky for you that this occurred at 200 feet. As you notice you lost a 100 feet in only seconds. At one point you had a decent rate of over 1200 feet per minute. Had this happened a lot lower this would have most likely would not have been recoverable unless you recognized it early on. ​

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The way recognize this early is by the motor noise starts sounding choppy, and the copter starts to wobble. If caught early throttle is all you need. If cought late throttle may not be enough as discussed above with the altitude lost. That is why it is important to really watch what the copter is doing when bringing it down.​

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Shaun​