When I plan a mission I include an RTL command as the last line in the plan. Unfortunately the craft retraces the waypoints back to start instead of returning to launch directly. Does anyone know which parameter I need to change to correct this?
In this case, it seems that your drone is performing a SmartRTL instead of a RTL (The Smart RTL navigates back to home by the known points of the mission).
Be sure that you are really including a RTL command in your mission.
I really do not know if ardupilot has some kind of parameter to always call a Smart RTL instead of common RTL.