The minimum airspeed is set below 5 m/s

What ArduPilot says:

• PreArm: AIRSPEED_MIN too low (N < N)

AIRSPEED_MIN is the lowest airspeed the autopilot will ask for in the modes where it controls the throttle. It is used without an airspeed sensor too: the control gains are scaled by it, the stall prevention starts from it, and the plane counts as flying above 75% of it. It must be 5 m/s or more; the message shows your value and that limit. The default is 9 m/s.

What to do, most likely first

1. The value was set to 0 or guessed too low while setting up a small, slow plane.

   FixSet AIRSPEED_MIN about 20% above the speed at which your plane stalls in level flight, never below 5. Keep AIRSPEED_CRUISE above it and AIRSPEED_MAX at least half as much again as AIRSPEED_MIN.

2. The parameters came from another aircraft, or only part of a file was written.

   CheckParameter Compare & Migrate shows what differs from the file you meant to load.

   FixLoad the whole file again, or set the three airspeeds by hand.

Parameters to look at

Where to do it:Starting ParametersParameter Compare & Migrate