What caused my quadcopter flyaway?

Hi, everyone! This has happened once before (with a different drone), but it happened again today, and clearly my previous attempts to fix it did not work.

Essentially, I was flying an auto mission with a target velocity of 5 m/s, when it just shot upwards, and nothing I did could stop it. Eventually it stopped, and although I briefly was in control again, it ended up free falling into the ground from 115 meters.

I can’t find anything in the logs that could cause that. I’ve checked for GPS glitches (they only occur after it begins its rapid ascent), abnormal voltage/current readings (I was wondering if the Pixhawk lost power?), and everything else I can think of, but nothing seems to be at fault.

The only correlation I could find was that the pitch was deeper than at any other point in the flight, right when the drone took off, but it was only -29 degrees. With my other two (nearly identical drones), I’ve reached angles of up to -40 degrees without issues. On the previous crash, the drone dipped to -41 degrees right when it took off upwards. On the other hand, it reached +47 degrees without problems.

Does anyone have any ideas as to why this happened? Here’s a link to the log:

Zipped logfile

Thanks in advance!

The usual cause of vertical flyaways is vibration, and yours is no exception.

You can see here that once the clipping starts the altitude goes up.
I would then correlate this with direct IMU readings but you didn’t log any IMU values.

I would guess the copter fell apart in flight. I am sure its hard to check now perhaps you could find something lose.

So what’s the physical mechanism behind vibration causing a flyaway? Are power connections being shaken loose (temporarily)? Why does that cause it to shoot upwards of all directions?

Thanks for the quick responses!