Definitions, Classification, and Levels of Autonomy

[rczyba][✓ rczyba, 2025-10-12]

Autonomy of unmanned systems refers to their ability to self-manage, make decisions, and complete tasks with minimal or no human intervention. The scope of autonomy ranges from zero to full capability, often defined through models, and encompasses four fundamental functions: perception, orientation, problem-solving (planning), and action. Advances in autonomy enable unmanned systems to learn, adapt to changing environmental conditions, and perform complex tasks, driving innovation in various fields.

There are several ways to classify autonomy levels based on various criteria. In 2014, the American organization Society of Automotive Engineers (SAE) International adopted a classification of six levels of autonomous driving, which was subsequently modified in 2016. Based on a decision by the National Highway Traffic Safety Administration (NHTSA), this is the officially applicable standardization in the United States, which is also the most popular in studies on autonomous driving technologies in Europe.

To clarify the situation, SAE International has defined 5 levels of automation for autonomous vehicles, which have been adopted as an industry standard (see Figure 1).

• Level 0: The driver has full control of the vehicle and there are no automated systems.

• Level 1: Also known as “hands-on,” the driver controls all standard driving functions, such as steering, acceleration, braking, and parking. Some automated systems, such as cruise control, parking assist, and lane-keeping assist, will be built into the car. The driver must monitor their surroundings and be able to take full control at any time.

• Level 2: “Hands-free” automation means that the automated system can take full control of the vehicle, steering, accelerating, and braking. However, the driver must be ready to take control of the vehicle if necessary. The “hands-free” principle shouldn't be taken literally, and the SAE recommends that the hands remain in contact with the steering wheel to confirm that the driver is ready to take control.

• Level 3: Level 3 is referred to as “without looking into the eyes” automation. The driver can focus on activities other than driving, such as using a phone or watching a movie. The automated system will be able to respond to situations requiring immediate action, such as emergency braking, but the driver will still need to intervene if notified by the technology.

• Level 4: The next level is “mind-off” automation. It's essentially similar to Level 3 in that the driver doesn't need to monitor their surroundings. In fact, they can fall asleep, as driver intervention isn't required, even in emergency situations. However, this level of autonomy is only supported in limited areas or under specific circumstances, such as traffic jams.

• Level 5: Level 5 means “steering wheel optional.” The car is fully autonomous and requires no human intervention.

In general, autonomy or autonomous capability is defined in the context of decision-making or self-governance within a system. According to the Aerospace Technology Institute (ATI), autonomous systems can essentially decide independently how to achieve mission objectives, without human intervention ^[2]. These systems are also capable of learning and adapting to changing operating environment conditions. However, autonomy may depend on the design, functions, and specifics of the mission or system ^[3]. Autonomy can be broadly viewed as a spectrum of capabilities, from zero autonomy to full autonomy. The Pilot Authorization and Task Control (PACT) model assigns authorization levels, from level 0 (full pilot authority) to level 5 (full system autonomy), also used in the automotive industry for autonomous vehicles (see Figure 2).

Levels of autonomy in drone technology are typically divided into five distinct levels, each representing a gradual increase in the drone's ability to operate independently.

• Level 0: The pilot has complete control over every movement. The platforms are always 100% manually controlled.

• Level 1 – Remote Control: The pilot retains control of overall operations and vehicle safety. However, the drone can take over one or more essential functions for a specified period. While the pilot does not have continuous control of the vehicle and never simultaneously controls speed and direction, it can assist with navigation and/or maintain altitude and position. The drone is supported by GNSS for flight stabilization, and all inputs regarding direction, altitude, and speed are entered manually. Obstacle detection functions are available at this level, but avoidance is performed manually by the pilot.

• Level 2 - Automated Flight Control (Assisted Autonomy): A pre-programmed flight path is transmitted to the autopilot, and the drone begins its mission, flying along waypoints. The pilot is still responsible for the safe control of the vehicle and must be ready to take control of the drone if an unexpected event occurs. However, under certain conditions, the drone itself can take control of the drone’s heading, altitude, and speed. The pilot still has full control, including monitoring airspace, flight conditions, and responding to emergencies. Most manufacturers currently build drones at this level, where the platform can assist with navigation functions and allow the pilot to disengage from certain tasks.

• Level 3 - Partial Autonomy (Semi-Autonomous): Similar to Level 2, the drone can fly autonomously, but the pilot must be alert and ready to take control at any time. The drone notifies the pilot of the need for intervention, acting as an emergency system. This level means that the drone can perform all functions “under certain conditions.”

• Level 4 - Cognitive Autonomy (Advanced Semi-Autonomous): A drone can be controlled by a human, but it doesn't always have to be. Under the right conditions, it can fly autonomously at all times. It's expected that the drone will have redundant systems so that if one system fails, it will continue to operate. At this level of autonomy, the “sense and avoid” function becomes “sense and navigate.” This means that the drone detects obstacles along its flight path and actively avoids contact by changing its flight trajectory.

• Level 5 – Full Autonomy: The drone controls itself independently in any situation, without the need for human intervention. This includes full automation of all flight tasks in all conditions. Currently, such drones do not yet exist. However, it is expected that in the near future, they will be able to utilize artificial intelligence tools for flight planning—in other words, autonomous learning systems with the ability to modify routine behavior.

Another general but useful model describing autonomy levels in unmanned systems is the Autonomy Levels for Unmanned Systems (ALFUS) model ^[5]. European Union Aviation Safety Agency (EASA), in one of its technical reports, provided some information on autonomy levels and guidelines for human-autonomy interactions. According to EASA, the concept of autonomy, its levels, and human-autonomous system interactions are not established and remain actively discussed in various areas (including aviation), as there is currently no common understanding of these terms ^[6]. Since these concepts are still somewhat developmental, this becomes a huge challenge for the unmanned aircraft regulatory environment as they remain largely unestablished.

The classification of autonomy levels in multi-drone systems is somewhat different. In multi-drone systems, several drones cooperate to perform a specific task. Designing multi-drone systems requires that individual drones have an increased level of autonomy. The classification of autonomy levels is directly related to the division into flights performed within the pilot's or observer's line of sight (VLOS) and flights performed beyond the pilot's line of sight (BVLOS), where particular attention is paid to flight safety. One way to address the autonomy issue is to classify the autonomy of drones and multi-drone systems into levels related to the hierarchy of tasks performed ^[7]. These levels will have standard definitions and protocols that will guide technology development and regulatory oversight. For single-drone autonomy models, two distinct levels are proposed: the vehicle control layer (Level 1) and the mission control layer (Level 2), see Figure 4. Multi-drone systems, on the other hand, have three levels: single-vehicle control (Level 1), multi-vehicle control (Level 2), and mission control (Level 3). In this hierarchical structure, Level 3 has the lowest priority and can be overridden by Levels 2 or 1.