2 The heartbeat message shows that a system is present and responding. The type of the MAV and Autopilot hardware allow the receiving system to treat further messages from this system appropriate (e.g. by laying out the user interface based on the autopilot). Type of the MAV (quadrotor, helicopter, etc., up to 15 types, defined in MAV_TYPE ENUM) Autopilot type / class. defined in MAV_CLASS ENUM System mode bitfield, see MAV_MODE_FLAGS ENUM in mavlink/include/mavlink_types.h Navigation mode bitfield, see MAV_AUTOPILOT_CUSTOM_MODE ENUM for some examples. This field is autopilot-specific. System status flag, see MAV_STATUS ENUM MAVLink version