How far can you really see the drone?
Introduction
Maintaining visual line of sight (VLOS) of a drone is a fundamental requirement under 14 CFR Part 107, which governs the commercial use of small unmanned aircraft systems (sUAS) in the United States. According to these regulations, drone pilots (or their visual observers) must always be able to see their aircraft unaided by any device other than corrective lenses. This requirement serves as a critical safety measure: by keeping the drone in sight, operators can better avoid collisions with buildings, power lines, or other aircraft, and can respond more quickly to unexpected events or emergencies.
In practical terms, “visual line of sight” means that the operator or observer can clearly identify the drone’s orientation and location in real time. While this may sound straightforward, factors such as distance, weather conditions, obstacles, and lighting can all compromise VLOS. Consequently, ensuring VLOS compliance across varying operational scenarios is not always a simple task.
Despite its importance, relatively little research has been dedicated to developing systematic methods to estimate or verify VLOS. Most current industry practices rely on manual observation and conservative flight planning to ensure the drone remains within sight, but these approaches can be subjective and prone to human error.
An example of for a multi-rotor drone (Autel Evo II v3) and a fixed-wing drone (AgEagle eBee) can be found below. A third panel provides the user with an interactive UI to enter in an arbitrary drone size and type for analysis.
While the EASA guidelines suggest a max visibility range of 601 ft, the use of visual acuity presents a recommended distance of no more than 850 ft with the limit of the average human’s vision at 1970 ft.
The variation is significant when comparing results for fixed-wing UAS. The EASA guidelines suggest a max visibility range of 1965 ft, the use of visual acuity presents a recommended distance of no more than 1482 ft with the limit of the average human’s vision at 2952 ft.