Flyaway - Potential Thrust Loss

I’d appreciate any insights into the events around 405 seconds in the attached log.

The quad was flying in AltHold at ~20mph. I then wanted to descend so I brought the pitch back to neutral and dropped the throttle close to zero. There was a GPS glitch and EKF error (maybe due to the abrupt change in attitude?), and right after that a “Potential Thrust Loss” message. The motors all went to maximum and the quad started to climb rapidly, even though I had the throttle at minimum.

In a semi-panic I tried several things, and there was another thrust loss message at 423 seconds.

I have two questions …

  1. What exactly caused this? Was I wrong to drop the throttle so far and so abruptly? Are there situations where lowering the throttle is close to zero will trigger a thrust loss error?

  2. When this happens, what’s the recommended way to recover?

Log here.

Thank you.

P.S. this was 3.7, so if the answer is don’t run pre-release s/w that’s fine too.

It looks very much like a mechanical failure.
Have a look at your IMU plot and compare that with the voltage and current.
There was an event that happened just before it took off.

In all cases like this it is switching to Stabilise that usually, usually, saves the day.
A bad vibration event in Alt hold will cause a climb.

Thank you for replying. This quad does have vibrations over 30 at times in fast forward flight, and after just watching Paul’s EKF logging video from the conference I have a better appreciation of why this is bad.

However I don’t see any event preceding the loss of control. The quad was in stable forward flight for ~10 seconds, and then the first sign of trouble in the logs is the signal to all four motors abruptly going to nearly max. At the time this happened all control inputs were constant, the altitude and speed were constant, and vibrations are fairly constant. All the bad things in the log like rising EKF innovations and the GPS glitch are logged right after the motors went to max. Is this order of things to be expected?