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Important Update: How to Calculate VLOS distance

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Visual line of sight operation (VLOS) was defined as a type of UAS operation in which, the remote pilot is able to maintain continuous unaided visual contact with the unmanned aircraft, allowing the remote pilot to control the flight path of the unmanned aircraft in relation to other aircraft, people and obstacles for the purpose of avoiding collisions. 

This brought many interpretations. That’s why in the latest version there’s a new way to calculate VLOS in a more accurate way.

Factors Influencing VLOS

  • Visibility: The operational area and weather conditions should allow the pilot to maintain unaided visual contact with the UA. A minimum visibility of 5km is recommended.
  • Size of the UA: Larger UAs are generally easier to see and track.
  • UA Characteristics: This includes aspects like the color of the UA (and how it contrasts against the background) and the brightness of its lights.

Calculating the new VLOS Distance

Calculating the new VLOS Distance The VLOS distance can be determined using two key parameters: the Attitude Line of Sight (ALOS) and the Detection Line of Sight (DLOS). The VLOS distance is the smaller of these two values.

1. Attitude Line of Sight (ALOS):

  • For rotorcraft and multirotor UA: ALOS [m] = 327 x CD [m] + 20m
  • For fixed-wing UA: ALOS [m] = 490 x CD [m] + 30m
  • CD refers to the characteristic dimension of the UA.

2. Detection Line of Sight (DLOS):

  • DLOS [m] = 0.3 x Ground Visibility
  • Ground visibility should be at least 5 km.

3. Defining the VLOS Distance:

  • The VLOS distance is the smaller value between ALOS and DLOS.


Understanding and accurately calculating the VLOS distance is fundamental for the safe operation of unmanned aircraft. By considering factors such as visibility, UA size, and specific characteristics, pilots can ensure they are operating within regulatory guidelines and maintaining safety in the airspace. As the use of unmanned aircraft continues to grow, adherence to these guidelines will become increasingly important for both hobbyists and professionals in the field.