Ac45 use it without gps and compass on quad racer

Hello, I just want to use AC45 for flight a little racer without GPS and compass on stab mode and althold only.

I make a first attemp flight desactivating completly compass and gps in EK3 src params and all seems working well.

But I experienced and EK3 failsafe.

What parameter I need to adjust to avoid that?
or for this setup you advice to use ek2 or ahrs?

Please let me know.

How to for use of dcm?