Wie weit reicht VLOS? Wie berechnet man die „Sichtverbindung“?

In the era of UAVO qualification certificates, the VLOS (Visual Line of Sight) distance was considered a difficult quantity to determine clearly, as it is influenced by numerous variable factors. However, since 2021, EU-wide harmonized drone flight rules apply. Following a proposal by the German Federal Aviation Office (LBA), the European Union Aviation Safety Agency (EASA) has published precise guidelines for calculating the VLOS distance with an accuracy of a few meters.

Holger Glur

Author

Regulations Regulations – open category (A) Regulations – special category (STS/S) For amateurs For professionals

05/08/2025

VLOS according to EASA – Definition & Calculation (Summary)

In this article, you will learn:

1. What VLOS means according to EASA (UA & airspace visually, avoid close approaches).
2. How the VLOS distance is determined via ALOS (size) and DLOS (visibility) – the smaller value applies.
3. Which formulas EASA specifies and what they mean in practice.
4. Short examples (DJI Mini 4 Pro, DLOS at 5 km) plus a note on horizontal range.

Definition (EASA)

VLOS is present when the pilot can scan the sky for aircraft, visually detect the UA, and avoid close approaches to aircraft, obstacles, or people. In OPEN, minimum distances on the ground (A2/A3) must also be monitored.

Calculation

VLOS is the line of sight between the pilot and the UA. Two characteristic values must be determined; the smaller one is decisive:

– ALOS (Attitude Line of Sight) – the distance from which the drone's attitude/orientation is still recognizable (dependent on CD, the characteristic dimension).
– DLOS (Detection Line of Sight) – the distance from which other aircraft are detected in time (dependent on ground visibility).

Formulas (EASA, Issue 2 – 04.10.2024)

ALOS Multicopter: ALOS [m]=327×CD [m]+20 ALOS Fixed-Wing: ALOS [m]=490×CD [m]+30 DLOS: DLOS [m]=0.3×GV [m] (max. GV usually 5 km in Airspace G)

Examples (brief)

– DJI Mini 4 Pro: CD≈0.27 m/0.40 m→ALOS≈108 m/≈151 m.
– DLOS: GV=5 km→1500 m; GV=1 km→300 m.

Horizontal Range at 120 m

horizontal= (VLOS 2 −Height 2 ) → With VLOS≈150 m and Height 120 m≈90 m.

Sources

– EASA: "Guidelines for UAS operations in the open and specific category", Issue 2 (04.10.2024).
– EASA: "Easy Access Rules – SORA". – LBA Guidance (Flight Geography & Ground Risk Buffer).
– Świat Dronów (Report on Issue 2).

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