GPS heading was lost in flight; the EKF fell back on the compass
What ArduPilot says:
- EKF3 IMUN yaw fallback active
- EKF3 IMUN yaw external
With EK3_SRC1_YAW 3 the EKF, ArduPilot's position and attitude estimator, takes its heading from a two-antenna GPS and keeps the compass in reserve. “yaw fallback active”: in flight, no GPS heading arrived for 10 s, and the compass had agreed with the GPS heading well enough before, so the EKF is now using the compass. “yaw external”: the GPS heading is back and in use again.
What to do, most likely first
The GPS lost its heading solution: one antenna is shaded in a turn, or reception dropped.
CheckIt comes during steep banks or near obstacles and “yaw external” follows within seconds.
FixIf it is rare and short, nothing. If it is frequent, give both antennas a clear view of the sky and check the antenna cables.
Parameters to look at
| Parameter | What it is |
|---|---|
EK3_SRC1_YAW | Yaw Source |
COMPASS_USE | Use compass for yaw |
The code that sends it
EKF3 IMUN yaw fallback active
libraries/AP_NavEKF3/AP_NavEKF3_MagFusion.cpp NavEKF3_core::SelectMagFusion() · Open in ArduPilot Copter-4.7.1
EKF3 IMUN yaw external
libraries/AP_NavEKF3/AP_NavEKF3_MagFusion.cpp NavEKF3_core::SelectMagFusion() · Open in ArduPilot Copter-4.7.1