6.1 Horizontal Separation Distances & Low-Speed Mode

Horizontal Separation Distances & Low-Speed Mode

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The Core A2 Horizontal Separation Rule

Under Commission Implementing Regulation (EU) 2019/947, Annex Part A, point UAS.OPEN.030(1), operations in subcategory A2 must be conducted such that the unmanned aircraft does not fly over uninvolved persons and maintains a safe horizontal distance of at least 30 m from them.

How the Distance Is Measured (AMC1 UAS.OPEN.030(1))

• The horizontal distance is measured from the point where the UA would hit the ground if it fell vertically (the point directly below it) to the position of the uninvolved person.
• As a reference, the lateral distance should be at least equal to the flying height (the 1:1 rule, covered in Section 6.2).
• In any case, the distance should always be greater than 5 m when low-speed mode is activated and set to 3 m/s, 5 m when operating a UAS balloon or airship, and 30 m in all other cases.
• GM1 UAS.OPEN.030(1) adds that the safe distance varies with the UAS's performance and characteristics, the weather and the segregation of the overflown area, and that the remote pilot is ultimately responsible for deciding it.

Why a 30-Metre Buffer Makes Sense

The regulation does not explain how 30 m was chosen, but three physical and human factors show why a buffer of this size is sensible:

1. Human Reaction Time: An average remote pilot requires approximately 1.0 to 1.5 seconds to perceive an unexpected flight anomaly, recognize the trajectory deviation, decide on an evasive control input, and physically move the transmitter gimbals.
2. Aerodynamic Deceleration & Braking Distance: A multirotor traveling at typical cruising speeds (12 to 15 m/s, or 43 to 54 km/h) requires between 10 and 18 m of clear airspace to come to a complete, stabilized aerodynamic stop once full reverse pitch/roll is commanded.
3. GPS Drift and Environmental Wake: In urban environments where satellite signals may experience multipath interference or where sudden wind gusts buffet the airframe, position-hold controllers can drift several meters before correcting.

A Class C2 unmanned aircraft with an MTOM of up to 4 kg moving at standard cruising velocity carries substantial kinetic energy ($E_k = \frac{1}{2}mv^2$): at 15 m/s, a 4 kg drone possesses 450 Joules of kinetic energy. Impact at this energy level is capable of inflicting fatal blunt-force trauma or severe skull fractures. The 30 m margin gives a fast-moving aircraft room to stop, or to be steered or fall clear of people, if propulsion or control is suddenly lost.

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The Reduced 5-Metre Low-Speed Mode Exception

Point (1) of UAS.OPEN.030 provides a vital operational flexibility: the standard 30 m horizontal distance may be reduced to a minimum of 5 m from uninvolved persons, but ONLY IF three strict, cumulative regulatory criteria are satisfied:

+-------------------------------------------------------------------------+
|       CUMULATIVE PREREQUISITES FOR REDUCED 5 METRE SEPARATION           |
+-------------------------------------------------------------------------+
| 1. AIRCRAFT CONFORMITY:                                                 |
|    Must be a Class C2 UAS bearing the C2 class identification label.    |
|                                                                         |
| 2. ACTIVE LOW-SPEED MODE:                                               |
|    Remote pilot must actively engage the drone's low-speed mode switch, |
|    which limits the aircraft's ground speed to <= 3 m/s.                |
|                                                                         |
| 3. PILOT RISK EVALUATION:                                               |
|    Pilot must evaluate ambient wind, gusts, UAS performance, payload    |
|    envelope, and the segregation/escape routes of the overflown area.   |
+-------------------------------------------------------------------------+

Condition 1: A Class C2 Aircraft

A2 operations require a UA marked as Class C2 and complying with that class, with Direct Remote ID and geo-awareness active and updated (UAS.OPEN.030(3)). The transitional arrangements of Article 22 ended on 1 January 2024. Since then, legacy drones without a class label may fly in the open category only in A1 (MTOM below 250 g) or A3 (MTOM below 25 kg) under Article 20, never in A2. Some manufacturers have brought existing models into a class through an official conformity process; only a drone that actually carries the C2 label qualifies.

Condition 2: Active Engagement of Low-Speed Mode ($\le 3\text{ m/s}$)

Under Part 3 of the Annex to Regulation (EU) 2019/945, a Class C2 UAS must be equipped with a selectable low-speed mode that limits the maximum horizontal ground speed to no more than 3 m/s (approximately 10.8 km/h).

Crucially, low-speed mode is not automatic. It must be explicitly commanded by the remote pilot (typically via a dedicated physical switch or software toggle on the flight controller). If the remote pilot operates at 3.5 m/s or leaves the flight controller in standard "Position" or "Sport" mode, the 5 m rule is void, and flying closer than 30 m constitutes an immediate regulatory violation.

At 3 m/s, the kinetic energy of a 4 kg drone drops precipitously to just 18 Joules:

$E_k = \frac{1}{2} \times 4\text{ kg} \times (3\text{ m/s})^2 = 18\text{ J}$

This represents a 96% reduction in kinetic energy compared to 15 m/s cruising flight! Furthermore, at 3 m/s, braking distance drops to less than 1.5 m, enabling near-instantaneous hovering stops when manual or automated braking is applied.

Condition 3: Comprehensive Environmental and Performance Assessment

The pilot cannot simply flip the low-speed switch and assume the 5 m reduction is safe. The pilot must actively verify that:

• Weather Conditions: Wind and gusts must allow the aircraft to hold position precisely. Low-speed mode limits ground speed, not thrust, so the drone can still lean into the wind. A strong gust can still push it sideways faster than 3 m/s for a moment before the controller corrects, and that drift matters when you are only 5 m from someone.
• Performance of the Aircraft: Consider how the aircraft brakes and holds position with its current payload and battery state, and what its loss-of-link and failsafe behaviour would do near people.
• Segregation of Area: The surrounding space must permit uninvolved individuals to be monitored clearly without blind corners where pedestrians might step directly under the flight path.

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Uninvolved Persons vs. Involved Persons

A critical area of theoretical examination is the exact legal distinction between "involved" and "uninvolved" individuals under European aviation law.

Involved Persons: The Legal Definition

Under Article 2(18) of Regulation (EU) 2019/947, "uninvolved persons" are defined as persons who are not participating in the UAS operation or who are not aware of the instructions and safety precautions given by the UAS operator.

Guidance material (GM1 Article 2(18)) explains when a person may be considered involved. Before the flight, the person must:

1. Have given explicit consent (it may be verbal) to the UAS operator or remote pilot to be part of the UAS operation. Participation can be indirect, such as a spectator or someone who agrees to be overflown;
2. Have received clear instructions and safety precautions from the UAS operator or remote pilot on what to do if the UAS behaves unexpectedly.

The UAS operator must also make sure every involved person can follow the emergency procedures in time. In principle, an involved person:

• can decide whether or not to take part;
• broadly understands the risks;
• has reasonable safeguards in place during the operation; and
• is not excluded from the event or activity if they decide not to take part.

The pilot should ask simple questions to check that the instructions have been understood.

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Who Is Generally Uninvolved?

Casual awareness of the drone does not make someone involved. The following people are uninvolved unless each of them individually meets the conditions above:

• Spectators and Bystanders: People watching the drone take off or fly, even if standing behind temporary crowd tape or barriers;
• Ticket Holders: Attendees at an outdoor venue, sports match, or concert. Buying a ticket or entering an event where a drone is announced does not make a spectator an involved person. GM1 Article 2(18) says that a statement on the ticket, a public-address announcement or an advance email or text is not enough;
• General Workers: Construction workers or warehouse staff working on a job site who have not received the specific UAS flight safety briefing;
• Pedestrians Passing Notice Signs: A sign posted on a sidewalk stating "Warning: Drone Operations Overhead" does not convert members of the public into involved persons;
• Motorists in Traffic: Drivers and passengers in cars, buses, or trucks traveling on adjacent public roads.

Persons Inside Buildings or Vehicles

GM1 Article 2(18) says that people protected by a shelter, such as a roof, are not considered exposed to direct risk from a UA with an MTOM below 25 kg. Moving traffic still creates secondary hazards: a drone striking a windscreen, or simply distracting a driver, can cause sudden braking or a collision. Good practice is therefore to avoid flying over busy roads. People walking along a road or street are uninvolved persons.

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Absolute Prohibition on Overflying Uninvolved Persons

One of the most foundational principles in European drone law is that in subcategory A2, overflight of uninvolved persons is strictly forbidden at all times.

The "No Inadvertent Overflight" Standard in A2

Notice the critical legal contrast between Subcategory A1 and Subcategory A2:

• In Subcategory A1 with a Class C1 drone, if an uninvolved person unexpectedly steps underneath the aircraft, the pilot is expected to navigate away as quickly as possible, but brief, inadvertent transit is legally recognized and tolerated due to low kinetic impact thresholds (< 80 J).
• In Subcategory A2 with a Class C2 drone, no overflight is tolerated whatsoever. The remote pilot must proactively maintain situational awareness so that an uninvolved person never falls within the vertical projection of the aircraft.

Tactical Emergency Response to Area Incursions

If an uninvolved pedestrian wanders into the 30 m (or 5 m) safety perimeter while the aircraft is airborne:

1. Freeze Horizontal Flight: Instantly release directional cyclic/pitch controls to halt forward or lateral travel toward the pedestrian;
2. Climb or Translate Away: If altitude permits, execute an immediate lateral translation vector away from the individual toward an unoccupied sector; never descend toward an area where people are walking;
3. Hover and Re-evaluate: Maintain a stable hover outside the separation boundary. If the pedestrian remains within the operational volume, abort the mission and navigate to the pre-designated alternate landing site.