Bad Or No Terrain Data?

ArduPlane VTOL Plane
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IMG20220912235911
IMG202209122359111920×2560 926 KB

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Did you read through this:
https://ardupilot.org/plane/docs/common-terrain-following.html

And perhaps used the below tool to download data if the regular way via MP doesn’t work:
https://terrain.ardupilot.org/

You may also have to check your TERRAIN_ENABLE & TERRAIN_FOLLOW settings as required.

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Also if your FC has a microSD slot make sure you have a card install and working.