In return to launch (RTL) mode, the copter navigates from its current position to hover above the home position. The behavior of RTL mode can be controlled by several adjustable parameters. This page describes how to use and customize RTL mode.
When RTL mode is selected, the copter will return to the home location. The copter will first rise to RTL_ALT before returning home or maintain the current altitude if the current altitude is higher than RTL_ALT. The default value for RTL_ALT is 15m.
RTL is a GPS-dependent move, so it is essential that GPS lock is acquired before attempting to use this mode. Before arming, ensure that the APM’s blue LED is solid and not blinking. For a GPS without compass, the LED will be solid blue when GPS lock is acquired. For the GPS+Compass module, the LED will be blinking blue when GPS is locked.
RTL will command the copter to return to the home position, meaning that it will return to the location where it was armed. Therefore, the home position is always supposed to be your copter’s actual GPS takeoff location, unobstructed and away from people. For APM:Copter if you get GPS lock and then ARM your copter, the home position is the location the copter was in when it was armed. This means if you execute an RTL in APM:Copter, it will return to the location where it was armed.
Warning: In RTL mode the flight controller uses a barometer which measures air pressure as the primary means for determining altitude (“Pressure Altitude”) and if the air pressure is changing in your flight area, the copter will follow the air pressure change rather than actual altitude (unless you are within 6 meters of the ground and have SONAR installed and enabled).