Published On: May 24, 2023By

Explaining the differences between BVLOS, EVLOS, and VLOS drone operations

In unmanned aviation, the acronyms VLOS, EVLOS and BVLOS are frequently used. People often ask what they mean, especially if you are new to the aviation industry. Knowing what these terms mean is important. This will enable you to apply the correct procedures for each type of flight operation. BVLOS flights in particular have special requirements, but before going into details, let’s cover the basics.

Visual Line of Sight (VLOS)A VLOS drone flight is an operation where the pilot has visual contact with the drone throughout the entire flight without the use of any visual aids. The maximum visibility depends on several factors, such as the size and color of the drone, the environment, the weather, and the time of day. Typically, the maximum visibility at which the drone can still be seen in the sky with the naked eye is around 500 metres (1640 ft), but this can vary depending on the factors mentioned above. During a VLOS flight, the pilot ensures that he or she maintains control of the drone and is able to detect and react to potential hazards such as other aircraft, obstacles, or people nearby.

The difference between VLOS, EVLOS and BVLOS by Unisphere The difference between VLOS, EVLOS and BVLOS

Extended Visual Line of Sight (EVLOS)

An EVLOS drone operation is a UAV flight in which the pilot cannot see the drone with the naked eye. One or more trained airspace observers support the drone pilot, usually via radio. This ensures continuous situational awareness of the airspace, and the drone pilot has direct control of the drone at all times. As several people are involved, communication is essential. The observers maintain visual contact with the drone throughout the flight, communicate with the pilot and alert him or her if necessary. This could also be done by technical solutions, e.g., the pilot can use additional solutions such as First Person View (FPV) devices to get a live camera feed of the surroundings. The detailed regulations for EVLOS flights can vary depending on the country and the purpose of the flight, but generally, operators must obtain permission and take certain safety precautions to ensure a low-risk operation.

Beyond Visual Line of Sight (BVLOS)

BVLOS is the extension of EVLOS. A BLOS operation is an UAV mission that takes place outside the visual line of sight of the remote pilot. This also means that the drone no longer has the protection of the pilot or observer to avoid terrain, obstacles and other aircraft. This requires extremely careful planning, because the drone needs to fly automated.


In VLOS and EVLOS drone operations, the radius of operations is limited, and therefore many opportunities for commercial use are eliminated (e.g. inspection of linear infrastructure, such as power line inspection along railways). To unlock the true economical potential of large-scale commercial drone operations, drone flights need to go beyond the line of sight.


A UAV operating in BVLOS mode no longer has the protection of the pilot or observer to avoid terrain, obstacles or other aircraft. Therefore, BVLOS operations require extremely careful planning by the operators.

In many countries, BVLOS operations are strictly regulated and obtaining permission is currently still a very complicated process. Aviation authorities are very strict about safety, especially because the drone industry is still an immature industry. The key to successful BVLOS approval is therefore to present a thorough and convincing safety case for your drone platform, justifying and explaining the processes to be followed during flight.


If a BVLOS operation takes place, the careful eyes of the pilot are useless, and it becomes necessary to use additional solutions to ensure safe flight operations. These include measures to prevent collisions between the drone and other aircraft as well as proper weather planning.

Good weather planning is not as simple as looking at different geographical locations. To ensure flight safety, weather planning needs to take place along the flight route and take into account different altitude profiles, as weather parameters such as wind can vary significantly with altitude. As a longer period of time can elapse between the take-off and landing of the drone, the time-lapse must also be taken into account when assessing the weather.

Unisphere offers various software solutions for evaluating weather conditions along a flight route as well as at a specific location to increase situational awareness. To learn more, check out our Blogpost about our 4D trajectory technology.