January 24, 2022 | Educational

VLOS, EVLOS and BVLOS – what is the difference?

The acronyms VLOS, EVLOS and BVLOS are commonly used in the world of unmanned aerial vehicles and their systems –, but often questions arise on what each of them actually mean and how to evaluate to match it to your planned flight mission.

Let’s begin with a closer look at each of these terms.

VLOS stands for Visual Line of Sight, meaning that the drone during the entire flight mission must be clearly visible by the drone operator without any additional aid – equipment such as binoculars, FPV goggles etc. The operator monitors the area and controls the UAV to avoid any collisions or obstacles.

EVLOS stands for Extended Visual Line of Sight. This allows to operate a drone further than VLOS by using one or more visual observers. The observers must be trained and instructed. During the flight observers keep a visual contact with the drone and communicate with the drone operator about observations and alerts the pilot if necessary.

BVLOS stands for Beyond Visual Line of Sight. In this mode, the drone operator does not maintain visual contact with a drone at all times, and the drone is able to carry out a mission without assistance of observers. The drone operator uses a remote pilot station or ground control station to monitor and control the mission.


VLOS, EVLOS and BVLOS infographic

Why is it important to know the difference?

It is crucial to identify ahead of the flight type to the mission format to be able to plan and execute the mission as additional equipment may be required or, – observer support and even specific permits from the Aviation Authorities in the dedicated area.

Looking at some examples:

If your mission type is VLOS, but the area to cover is exceeding the VLOS range, you will have to consider doing several minor flights covering smaller areas in order be able to cover the full desired area. In such cases, it is reasonable to consider the use of EVLOS, but you must consider the need and availability of an observer, which may also imply additional costs, and time, both crucial factors. EVLOS will also require additional communication equipment to ensure communication quality during the flight. If limited with these resources, more efficient solution would be to just move around the area and use VLOS only.

BVLOS missions are the most complex of all the above as they hold additional safety aspects to consider and risks to mitigate. To carry out BVLOS flights you must obtain approval, which is not always easy to get. In most cases, it is required to prove that UAV and pilot qualify and are certified for BVLOS, and the mission itself does not carry risks or threats. Regulations and requirements also differ in each country and commonly BVLOS applications are evaluated case by case.

What distance is considered VLOS?

VLOS requires direct and clear eye contact with the drone. But how far it actually is?

According to EASA and FAA, the VLOS is not so much about the distance as it is about the ability to actually see the drone and be able to see and evaluate the surroundings to carry out a safe flight mission. A lot of aspects affect the real VLOS distance – the UAV size, the flight speed, weather conditions (fog, mist, snow, etc.), time of the day of the flight (dusk, dawn, etc.), eyesight of the drone operator, presence of tall objects in the flight area, and more. All listed factors affect visibility and therefore the VLOS.

However, based on the flight operators’ experience, the recommendation is not to exceed a distance over 500m (1640 ft) from the UAV to the drone operator to execute a safe flight and be aware of the surroundings.

But if a drone flies behind the visual obstacle within this range, it is no longer considered VLOS as the pilot loses direct visual contact with the drone.

 In which category does FPV fall?

Drone operators often use FPV – the first-person view – goggles to operate the drone. This allows a pilot to see the visual stream directly from the drone camera.

Even this allows to see real-time drone view, it doesn’t provide complete awareness of the surroundings of the aircraft, therefore FPV is not considered VLOS and requires an observer. This makes it fall under EVLOS.