Help with PX4 Autopilot Integration for Custom Fixed-Wing UAV

What do you mean with that? And I wonder whether this only starts working properly with airspeed. Try blowing with a fan on airspeed.

Isn’t this available with the existing parameters/settings? At least for multicopter it is.
See: Failsafe State Machine Simulation | PX4 Guide (v1.15)

Does this help?