Hi Folks -
First thanks to all the developers and the community at large who take time to look over logs and respond to end users like myself.
I’m just starting to dig into tuning/diagnosing, and have one that I’m stuck on: I have combed through the log file and simply cannot find the cause leading up to a sudden spike in my RCOU.C2 channel which resulted in the quad pitching suddenly into the ground. RCin was steady. Nearly everything I compare to this spike happen at the same exact time (e.g. mags, IMU, etc) so it’s tough to say if they are a cause or an effect.
Incident occurred around the 153,000 mark in the flash log. Around 0:16 in the video. Was running in Stabilize mode, simply idling. Vibration in spec, no physical/mecanical issues apparent (flew a few times after). I’m still weening myself off loiter/poshold so when in stabilize things are a little touchy for me (towards the end of the video it felt like it was getting away from me so I initiated a land).
-F450 frame, sunny motors, RTFquad ESCs (sorry no pn’s handy)
-Pixhawk clone running latest Copter
-3DR UBlox, mounted about an inch above Pixhawk (see picture, below link)
-X9D with X4R via SBUS,
I just read from another post that the internal mag should be disabled if using an external? In any case, here is a link to the logs, video, and quick picture of the setup:
https://drive.google.com/open?id=0B1k6-5Eu6OVdXzBwTHI1YUFwaWs
Oh and before you ask, yes there was a run-in with a tree at the end of the log. 
Thanks again for your time. As I mentioned I’m new to the log viewer and so maybe I’m simply not picking up on something.
Jamie