Is there a max initial altitude for SITL/FlightGear?

Is there a limit on altitude for SITL (or maybe FlightGear)? Mission and dronekit script work fine up-to 479m but when the initial position is >= 480m, the simulation does not start.

locations.txt: BEEF=55.404,-3.486,480,180 --out --console -L BEEF

ArduPlane 3.9.1 SITL


OK - So. It’s only for missions with absolute altitude waypoints. Terrain and relative missions work fine.