C-DRONE GUIDE · 2 SEPTEMBER 2026

EVLOS and the STS-02 scenario: flying beyond visual line of sight with a chain of observers along a linear corridor

A twelve-kilometre power line, a railway crossing three communes, a gas pipeline buried under dozens of kilometres of countryside: for that kind of route, flying in direct visual line of sight means dozens of successive take-offs. The STS-02 standard scenario offers another way: a chain of observers posted along the route relays the remote pilot's visual watch, and the drone moves beyond direct sight without ever escaping a human eye. Operators call this "EVLOS" — a word the regulation itself never uses. Since 1 January 2026, this is no longer one option among others: it is the only one left, the old national scenario that used to cover the same ground having ceased to exist at midnight on New Year's Eve. Here is how it works, its limits, and its 2026 price.

Published on 2 September 2026, reviewed on 5 September 2026 — regulations in force as of September 2026.

EVLOS, a word the regulation never uses but which describes STS-02 well

EU regulation 2019/947 recognises only two visibility regimes: visual line of sight (VLOS) and beyond visual line of sight (BVLOS). The word "EVLOS", for extended visual line of sight, appears in no French or European text — it is an industry term operators use to describe a BVLOS flight still watched by human eyes rather than handed over to a detect-and-avoid sensor. On the ground, that is exactly what the STS-02 standard scenario allows: a class C6 drone flies beyond the remote pilot's direct sight, but stays under the continuous watch of a chain of observers positioned along the route, each relaying visual airspace awareness to the next.

The framework is precise: a maximum height of 120 metres above ground, a sparsely populated area with no overflight of assemblies of people, and a total distance from the remote pilot capped at 2 kilometres — reached by spacing observers no more than 1 kilometre apart, each able to communicate with the pilot in real time. Every observer must hold the theoretical certificate common to the standard scenarios plus the practical attestation specific to STS-02; a simple operational declaration on AlphaTango is then enough, with no individual DGAC authorisation to wait for — see our guide to the open or specific category for where STS-02 sits within the wider regulatory framework.

1 January 2026: the end of the national scenarios closes a more flexible route

Until the end of 2025, an operator who wanted to survey a linear route beyond visual line of sight could rely on the national scenario S2, quicker to file than an STS. That route is gone: the national scenarios S1, S2 and S3 ceased to be valid at midnight on 31 December 2025, at the end of the transition period opened when the European standard scenarios entered into application on 1 January 2024. Since 1 January 2026, any operational declaration still tied to one of those scenarios has automatically shown as "not renewed" by the DGAC on AlphaTango — it no longer covers any flight.

For a BVLOS mission along a linear corridor, the consequence is concrete: an operator who was still working under the old S2 must have re-filed their fleet and operations manual under STS-02, with its own constraints — C6 class, observer chain, sparsely populated area — more strictly codified than S2 ever was. For a client, the check is simple: ask the provider which exact scenario covers their AlphaTango declaration for the site concerned, and be wary of a quote dated 2026 that still refers to "S2" — a sign the paperwork was never updated.

The limits of the observer chain: when a SORA authorisation is needed instead

STS-02 stops flat at 2 kilometres and a sparsely populated area: a corridor crossing a village, running alongside a busy road, or exceeding that distance falls outside the scope of a simple declaration. It then needs an operational authorisation based on a SORA risk assessment or a predefined risk assessment (PDRA), processed by the DGAC over several weeks to several months — a slower, costlier route to plan for from the specification stage, not once the flight is being scheduled.

That limit is not just administrative: a study by Maximilian Peukert and Christoph G. Santel, published in 2024 in the CEAS Aeronautical Journal, shows that a human observer, however attentive, does not always give the remote pilot a complete and reliable picture of the surrounding air traffic — hence the parallel development, alongside observer-based scenarios, of onboard detect-and-avoid systems for missions that exceed what human vigilance can reasonably cover (see the study on Google Scholar). For now, in France, those systems remain mostly used within a SORA authorisation: STS-02 itself stays bounded by what a chain of human eyes can reliably cover.

Which linear assets EVLOS genuinely changes things for

The clearest use case remains power line inspection and vegetation clearance under a high-voltage corridor: a section between two substations rarely exceeds the two kilometres covered by a chain of two or three observers, while a ground survey would tie up a crew for hours. A review by Van Nhat Nguyen, Robert Jenssen and Davide Roverso, published in 2018 in the International Journal of Electrical Power & Energy Systems, makes a point that still holds true today: aerial inspection of power networks has moved faster than the automation of the image analysis that follows it, with most fault sorting still a human task performed on the images brought back (see the study on Google Scholar).

Railway lines and gas pipelines share the same geometry: a long route, usually outside built-up areas, where positioning an observer every kilometre costs less than flying the same ground in several short VLOS hops. The one factor the scenario cannot control, though, is wind: on an exposed stretch, a local gust can break the observer chain before the flight itself even needs to stop.

Steps and price of an EVLOS mission in 2026

An STS-02 mission is prepared in three stages. First, checking the whole length of the route: population density, the presence of occasional gatherings (a market, an event), and scouting access points to position each observer along the way. Then, on the day: deploying the team, a radio check between every link in the chain before take-off, then moving the drone link by link to the end of the route. Finally, processing the images or the thermal pass, and handing the results to the asset manager. The regulatory information on this page reflects the rules in force in September 2026.

Orders of magnitude observed in 2026 (excl. VAT):

For a route to be covered beyond visual line of sight, whether for a network operator, a local authority or an industrial operator, request a quote stating the exact length of the route and the population density it crosses: those two facts determine whether STS-02 is enough or a SORA authorisation is needed.

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