The Open category of operations, referred to as „Open“, is a basic category for flying drones established by European legislation. It includes flights that present a low level of risk to uninvolved persons and property on the ground, and therefore do not require prior authorization from the Civil Aviation Authority. The pilot must always maintain direct visual line of sight with the drone and fly at a maximum height of 120 meters above the ground. The category is further divided into three subcategories (A1, A2, A3), which further specify the rules according to the drone's weight and its technical certification. These subcategories determine how close it is possible to fly to people, populated areas, or buildings. For most flights in this category, registration of the drone operator and passing an online pilot test are required.