Visual line of sight distance

Model: ALOS = 327·CD + 20 m (multirotor) or 490·CD + 30 m (fixed wing); DLOS = 0.3·GV, with GV counted up to 5 km (LBA); VLOS = min(ALOS, DLOS). EASA recommends a ground visibility of at least 5 km

Show your work

1. Where you can still see the aircraft

   ALOS from the characteristic dimension, per the EASA procedure

   0.35 m across = 134 m

2. Where the air is still clear enough

   DLOS = 0.3 × ground visibility

   0.3 × 5,000 m = 1,500 m

3. Visual line of sight

   VLOS = the smaller of the two

   the smaller of 134 m and 1,500 m = 134 m

The same steps an agent gets from the MCP server with explain: true.

Accuracy: Guidance values for planning, not a guarantee you will see the drone.

When to use this: Use this when planning a flight you have to keep in sight: it gives the distance at which the aircraft's attitude is still readable, the distance at which it can still be detected in the visibility you have, and the smaller of the two, checked against the farthest point of your planned area.

Limitations: These are the EASA guidance formulas for planning, not a promise that you will see the aircraft. They depend on the characteristic dimension you enter and on the visibility, and they say nothing about the sun's position, the background you are looking against, an observer's eyesight, or obstacles in the way. The rule you fly under, and your own judgement in the moment, govern.

Worked example: A 0.35 m multirotor with a mission 400 m out. Source: add-practitioner-essentials VLOS scenario: ALOS 134 m (327 × 0.35 + 20); beyond VLOS guidance by 266 m.

Review: Not yet independently reviewed by a Part 107 remote pilot.

Last verified: 2026-09-23, when a maintainer last confirmed this tool's sources at the issuer. See the sources ledger.

Status: version 1.2.0, core 0.1.0. See this tool in the verification report.

Changes

• 2026-09-23, fixed: Visual line of sight (version 1.2.0) now warns when the ground visibility is below 5 km, the least EASA's guidelines recommend. It gave no warning at 1 km or 0.3 km. Above 5 km it still counts only 5 km, but it now credits that cap to the LBA guidance EASA points to, and cites it; it wrongly called 5 km the most the EASA procedure assumes. No distance changes. Changelog
• 2026-09-19, fixed: VLOS guidance now takes ground visibility as at most 5 km, as EASA's procedure and the German LBA guidance assume, so VLOS never exceeds 1,500 m. Without a visibility it used only the aircraft's size, so a 10 m multirotor showed 3,290 m. It is now stable, matching the LBA's worked table, and cites EASA's guidelines at Issue 03 (17 July 2025). Tool version 1.1.0. Changelog

Checked against: 25 golden test vectors (download the test vectors, each with its source and tolerance). See how results are checked and every source.

Sources

• Guidelines for UAS operations in the open and specific category, European Union Aviation Safety Agency, Issue 03, 17 July 2025. Part A, chapter I, VLOS distance: ALOS = 327 × CD + 20 m (multirotor), 490 × CD + 30 m (fixed wing); DLOS = 0.3 × ground visibility.
• Guidance for Dimensioning of Flight Geography, Contingency Volume and Ground Risk Buffer, Luftfahrt-Bundesamt (LBA), Revision 1.7, 26 November 2024. Section 7 (DLOS limit: GVmax = 5 km) and section 7.1 (maximum VLOS distance table, valid for 5 km visibility or more).

Terms

ALOS: attitude line of sight

The farthest distance at which a remote pilot can still see a drone's position and orientation. EASA ties it to the drone's size. Source: EASA Guidelines for UAS operations in the open and specific category

DLOS: detection line of sight

The distance at which other aircraft can be seen in time to avoid them. EASA takes it as 0.3 times the ground visibility. Source: EASA Guidelines for UAS operations in the open and specific category

EASA: European Union Aviation Safety Agency

The EU agency that sets aviation safety rules, including the drone rules in Regulations (EU) 2019/947 and 2019/945. Source: EASA Guidelines for UAS operations in the open and specific category

VLOS: visual line of sight

Flying where the remote pilot can see the drone without aids. EASA's acceptable distance is the smaller of ALOS and DLOS. Source: EASA Guidelines for UAS operations in the open and specific category