6.2 Visual Line of Sight (VLOS), Follow-Me Limits & FPV with Observers

6.2 Visual Line of Sight (VLOS), Follow-Me Limits & FPV with Observers

[!NOTE] The Bedrock of Open Category Safety: Point UAS.OPEN.060(2)(b) and Article 2(7) of Commission Implementing Regulation (EU) 2019/947 establish that the remote pilot shall maintain continuous Visual Line of Sight (VLOS) with the unmanned aircraft throughout the flight, except when operating in follow-me mode or when an unmanned aircraft observer assists in FPV operations. VLOS is the primary collision avoidance safeguard in low-altitude civil aviation.

The Open category is built upon the foundational assumption that the remote pilot can see the unmanned aircraft, perceive its position and trajectory, detect potential conflicting aircraft or obstacles, and manually maneuver to avoid collisions. Losing sight of the aircraft instantly nullifies this safety layer, transforming the operation into an unauthorized Beyond Visual Line of Sight (BVLOS) flight that requires Specific category authorization.

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The Legal Anatomy of Visual Line of Sight (VLOS)

Article 2(7) of Regulation (EU) 2019/947 establishes a precise, binding definition of VLOS:

"'Visual line of sight operation' (VLOS) means an 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, boats and structures for the purpose of avoiding collisions."

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|                           THE FOUR PILLARS OF LEGAL VLOS                          |
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| 1. CONTINUOUS CONTACT   -> The pilot must keep the drone in active visual scan;   |
|                            momentary glances down at telemetry are acceptable,    |
|                            staring exclusively at a screen is a legal violation.  |
| 2. DIRECT & UNAIDED     -> Direct line of sight with the naked eye. Only normal   |
|                            vision correction (glasses/contacts) is allowed.       |
| 3. FLIGHT PATH CONTROL  -> The pilot must be able to discern the aircraft's      |
|                            orientation, heading, pitch, and bank angle.           |
| 4. COLLISION AVOIDANCE  -> The pilot must visually scan surrounding 3D airspace   |
|                            to yield right-of-way to all manned aviation.          |
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Permitted vs. Prohibited Optical Aids

European air law explicitly distinguishes between corrective medical optics and artificial magnifying devices:

• Permitted Visual Aids:
  • Corrective Eyeglasses (Spectacles): Normal prescription lenses used to correct myopia, hyperopia, or astigmatism are fully permitted.
  • Contact Lenses: Both soft and rigid gas-permeable corrective contact lenses are fully permitted.
  • Non-Polarized or Polarized Sunglasses: Permitted to reduce atmospheric haze and glare, provided they do not impair color perception of aircraft lights.
• Strictly Prohibited Devices for Primary VLOS:
  • Binoculars & Monoculars: While magnification enlarges the aircraft, it narrows the field of view to a tiny optical tube, destroying the pilot's peripheral situational awareness and making it impossible to detect incoming aircraft or track rapid drone maneuvers.
  • Telescopes & Spotting Scopes: Prohibited for primary VLOS maintenance.
  • Night-Vision Goggles & Electronic Viewfinders: Prohibited as primary VLOS tools.
  • Smart Device / Tablet FPV Screens: Staring continuously at a video transmission feed displayed on a smartphone or monitor does NOT constitute VLOS.

[!IMPORTANT] Exam Distinction — Binoculars in Operations: An airspace observer may use binoculars for a brief, intermittent second to confirm the identity or flight direction of a distant manned aircraft spotted in the distance. However, binoculars can never be used by the pilot or observer to maintain, re-acquire, or extend the legal VLOS range of the drone!

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Practical Determinants of Maximum VLOS Distance

Many remote pilots mistakenly believe that if they can still see a minuscule black dot on the horizon, they are flying legally in VLOS. Under EASA guidance material (GM1 Article 2(7)), this is false.

To exercise effective collision avoidance and flight path control, the remote pilot must not merely detect the presence of an airborne object; they must be able to discern its heading and spatial attitude (which way it is pointing, banking, and travelling). The moment a pilot cannot determine whether the drone is flying toward them, away from them, or drifting sideways, legal VLOS has ceased.

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|                   FACTORS GOVERNING EFFECTIVE VLOS RANGE                          |
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|   AIRCRAFT SIZE        |   CONTRAST & COLOR      |   ATMOSPHERIC CONDITIONS       |
| Small drone (<250 g)   | Dark airframe against   | Haze, humidity, and glare      |
| loses orientation at   | bright gray sky gives   | reduce contrast drastically.   |
| 100-150 m. A 25 kg UAS | high contrast; dark     | Flying toward the sun creates  |
| visible to 500+ m.     | against forest is lost. | blinding direct silhouetting.  |
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1. The Human Eye and Visual Acuity

The human eye has a theoretical angular resolution limit of approximately 1 arcminute (1/60th of a degree) for high-contrast objects under optimal lighting.

• For an object with a characteristic dimension of 30 cm (typical consumer quadcopter), 1 arcminute translates to a maximum detection limit of roughly 1,000 metres.
• However, resolving attitude and heading requires resolving details such as propeller arms, landing gear, and color orientation lights—which are 5 to 10 times smaller than the overall airframe.
• Consequently, for a typical 250 g to 1 kg drone, the practical limit for discerning orientation is rarely greater than 150 to 300 metres, even for individuals with 20/20 (6/6) visual acuity.

2. Physical Airframe Parameters

• Dimensions and Footprint: Larger aircraft (e.g. C3 or C4 class aircraft with a 1.5-metre wingspan or diagonal wheelbase) reflect more light and present a significantly larger retinal silhouette, extending practical VLOS out to 400–600 metres.
• Airframe Color and Livery: White drones easily disappear against overcast cloud layers; black or dark gray airframes disappear against dark terrain, treelines, or asphalt. Bright, high-visibility fluorescent schemes (aviation orange, neon yellow) maximize contrast across diverse backdrops.
• High-Intensity Strobe Beacons: Directional and anti-collision LED strobes substantially enhance detection range, particularly during twilight or overcast conditions.

3. Atmospheric and Environmental Visibility

• Sun Angle and Glare: Flying an unmanned aircraft along an azimuth directly into the sun creates extreme glare, blinding the pilot and instantly causing loss of visual contact. Standard SOP dictates orienting flight patterns with the sun behind or perpendicular to the pilot.
• Atmospheric Scattering: Particulate matter, smoke, dust, and humid haze scatter light rays (Mie scattering), washing out contrast and reducing effective visual range well before meteorological visibility drops below official thresholds.

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First Person View (FPV) Operations and the Unmanned Aircraft (UA) Observer

First Person View (FPV) flight involves flying an unmanned aircraft using an onboard video camera transmitting live real-time video to immersive video goggles or a head-mounted display worn by the remote pilot.

The Inherent Conflict of FPV Flight

When a remote pilot wears FPV goggles, their eyes are enclosed within a display unit. They perceive exclusively what the nose-mounted camera captures:

• The pilot's peripheral vision is 100% occluded.
• The forward camera has a fixed or limited field of view (often 110°–150°).
• The pilot cannot see what is above, below, behind, or to the sides of the drone.
• Most critically, the pilot cannot scan the surrounding airspace for approaching manned aircraft, nor can they see uninvolved pedestrians approaching the launch site.
• Therefore, a solo remote pilot wearing FPV goggles is physically and legally incapable of maintaining direct VLOS.

The Mandatory Legal Solution: The UA Observer

To accommodate FPV operations without compromising aviation safety, Commission Implementing Regulation (EU) 2019/947 Point UAS.OPEN.060(4) establishes a strict operational framework:

"When carrying out operations in the Open category using first-person view (FPV), the remote pilot shall be assisted by an unmanned aircraft observer."

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|                     LEGAL MANDATES FOR THE UA OBSERVER (UAS.OPEN.060(4))          |
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| 1. CO-LOCATION          -> Must stand physically directly alongside the remote    |
|                            pilot (side-by-side, within arm's length).             |
| 2. CONTINUOUS VLOS      -> Must maintain continuous, direct, unaided visual       |
|                            contact with the unmanned aircraft at all times.       |
| 3. DIRECT VOICE COMMS   -> Must communicate directly via unamplified voice.       |
|                            NO radios, walkie-talkies, cell phones, or headsets!   |
| 4. AIRSPACE SCANNING    -> Must actively and continuously scan the 3D airspace for|
|                            manned aircraft, helicopters, gliders, birds, clouds.  |
| 5. GROUND SURVEILLANCE  -> Must monitor ground hazards, approaching pedestrians,   |
|                            and obstacles along the drone's flight path.           |
| 6. IMMEDIATE WARNING    -> Must immediately instruct the pilot to alter course or |
|                            land if an air-risk or ground-risk conflict emerges.   |
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Observer vs Remote Pilot: Responsibilities Matrix

[!WARNING] Exam Trap — Observers Extending Range (BVLOS): A frequent exam trap suggests that a pilot can place visual observers on hilltops 1 kilometre away, communicating via two-way walkie-talkies to fly the drone over long distances. This is strictly ILLEGAL in the Open category. In the Open category, an observer is permitted ONLY for FPV flights, and the observer MUST stand directly beside the pilot. Using observers across a distributed chain to extend operational range constitutes a BVLOS operation, strictly reserved for the Specific category under Standard Scenario STS-02 or SORA!

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Follow-Me Mode Limits in Subcategory A1

Modern unmanned aircraft often feature automated tracking modes where the aircraft locks onto the remote pilot (or the pilot's control transmitter / smartphone) and autonomously tracks their movement while skiing, cycling, running, or driving.

Article 4(1)(d) and Point UAS.OPEN.020(3) define the precise boundaries under which autonomous follow-me operations are legally permitted in the Open category:

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|                        FOLLOW-ME MODE STATUTORY BOUNDARIES                        |
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|  1. Applicable Subcategory:  SUBCATEGORY A1 ONLY                                  |
|  2. Permissible Hardware:    Class C0 or Class C1 unmanned aircraft only          |
|  3. Weight Limit:            MTOM strictly under 900 grams                        |
|  4. MAXIMUM DISTANCE:        50 METRES (164 ft) maximum from the remote pilot     |
|  5. Pilot Responsibility:    Pilot must maintain continuous situational awareness |
|                              and be prepared to immediately resume manual control |
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Why the 50-Metre Boundary?

• Sensory and Acoustic Buffer: At distances within 50 metres, the remote pilot can clearly hear rotor acoustic feedback, monitor the aircraft's proximity to trees or terrain, and maintain rapid visual re-acquisition even while in physical motion.
• Reaction Time: If an unexpected bystander steps into the tracking path, or if the drone drifts toward a tree branch, the pilot must be able to take manual command of the transmitter immediately to halt forward progress.
• Ground Risk Mitigation: Limiting follow-me to lightweight C0 (<250 g) and C1 (<900 g) platforms ensures that even if an autonomous tracking collision occurs, kinetic energy remains below dangerous levels.
• Exceeding 50 Metres: If an aircraft operating in follow-me mode tracks a pilot beyond 50 metres, it violates Point UAS.OPEN.020(3). The operation ceases to be an authorized A1 follow-me flight and constitutes an illegal automated flight.

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Realistic Flight Scenarios: VLOS, FPV, and Follow-Me in Action

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| SCENARIO 1: High-Speed FPV Drone Racing in a Public Park                          |
| A remote pilot wants to fly an acrobatic FPV quadcopter using immersive goggles.  |
| - Operational Setup: The pilot enlists a friend to act as a UA Observer.          |
| - Legal Compliance: The observer stands directly at the pilot's elbow. Both       |
|   discuss emergency words ("LAND NOW", "TRAFFIC LOW"). The observer monitors  |
|   the quadcopter continuously with unaided vision while scanning for dogs and     |
|   park visitors. When an air-ambulance helicopter approaches at low altitude, the |
|   observer verbally alerts the pilot, who immediately descends and lands.         |
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| SCENARIO 2: Mountain Biker Filming a Downhill Descent                              |
| A mountain biker activates Follow-Me mode on a 550 g Class C1 drone.              |
| - Distance Parameter: The tracking distance is set to 30 metres behind the bike.  |
| - Airspace & Ground Check: The trail is clear of pedestrians and overhead wires.  |
| - Regulatory Assessment: Flown fully legally within Subcategory A1, as distance   |
|   remains strictly under the statutory 50-metre cap and aircraft is under 900 g.  |
|   Had the pilot set the tracking radius to 75 metres, the flight would be illegal.|
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Common Exam Traps & Pitfalls

• Trap: Optical Zoom and Monitors Count as VLOS: Exam questions frequently ask if viewing a crystal-clear 4K live feed on a 10-inch high-brightness monitor constitutes VLOS. The answer is NO. VLOS requires direct, unassisted line of sight to the physical aircraft in the sky.
• Trap: Distance Observers with Radios in Open Category: Questions often describe a pilot placing an observer on a ridge 800 metres away with a VHF walkie-talkie. In the Open category, this is STRICTLY PROHIBITED. The observer must stand right next to the pilot and communicate directly via voice.
• Trap: Binoculars Permitted for Maintaining VLOS: Remember that binoculars are prohibited for maintaining primary VLOS. They severely restrict situational awareness and eliminate 3D peripheral scanning.
• Trap: Follow-Me Mode Permitted Up to 120 Metres: Many candidates confuse the 120-metre maximum altitude ceiling with the follow-me distance limit. Follow-me mode is capped at 50 metres horizontal distance from the pilot.
• Trap: Follow-Me Permitted in Subcategory A3 with C3 Drones: Follow-me mode under Point UAS.OPEN.020(3) is an A1 privilege restricted to C0 and C1 aircraft (<900 g). You cannot use follow-me mode with a 15 kg C3 drone in Subcategory A3 while jogging through a public area.