GPS failure -> plane nose dive

Hi all!

Few days ago we experienced anomaly and loss of aircraft during low altitude mapping mission.

Setup and params (might be inaccurate):

Fixed wing plane
Cube orange running plane 4.0.9 stable
Here 2 as GPS1 and Compass
Ublox RTK GNSS with external antenna as GPS2

EK3_ALT_SOURCE was set to GPS
GPS_AUTO_SWITCH was set to Use best

About 30 minutes in the GPS2 failed. Sat count dropped from 35 to around 10 and we got horizontal and vertical position variance errors as expected. Altitude estimation jumped from nominal 35 m to 160 m in less than a second. Plane reacted by reducing power and doing steep nose dive and crashed into a lake.

To my understanding EKF3 should do better than that? It should be easy to tell from IMUs and barometric pressure that such a altitude jump is not possible and GPS data is faulty.

Our older mapping planes with older arduplane versions running EKF2 have survived similar anomalies and were successfully returned to home in manually triggered RTL.

We did recover the wreck but its still unclear if the autopilot and its log files survived.