6.3 Night Flight Rules & Green Flashing Light Requirements

6.3 Night Flight Rules & Green Flashing Light Requirements

[!NOTE] Open Category Night Operations: Unlike earlier fragmented national laws that outright banned drone operations after sunset, Commission Implementing Regulation (EU) 2019/947 fully authorizes night flights in the Open category across all EU Member States, provided specific technical lighting requirements are met and local UAS geographical zones do not impose night restrictions.

Operating an unmanned aircraft at night introduces profound operational, aerodynamic, and human-factor challenges. The natural visual cues that remote pilots rely on during daylight—horizon reference, terrain contours, tree branches, power lines, and surface texture—vanish in the dark. To mitigate collision hazards with manned aircraft and ground obstacles, European regulations mandate specific lighting configurations and disciplined flight procedures.

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The Legal Definition of Night in European Aviation

To comply with aviation law, remote pilots must know precisely when "night" begins and ends. Under the definitions in Article 2 of Commission Implementing Regulation (EU) No 923/2012 (the Standardised European Rules of the Air, commonly known as SERA) — a definition Regulation (EU) 2019/947 adopts by reference in its own Article 2(34) — night is defined with astronomical precision:

"'Night' means the hours between the end of evening civil twilight and the beginning of morning civil twilight, or such other period between sunset and sunrise as may be prescribed by the appropriate authority."

+-----------------------------------------------------------------------------------+
|                        THE ASTRONOMICAL PROGRESSION OF NIGHT                      |
+-----------------------------------------------------------------------------------+
| DAYLIGHT            -> Sun is above the horizon. Full natural illumination.       |
| SUNSET              -> The moment the upper edge of the sun's disc touches horizon|
| CIVIL TWILIGHT      -> Sun is between 0° and 6° below the true horizon.           |
|                        Natural light is sufficient for ordinary outdoor activities|
|                        without artificial lighting.                               |
| END OF CIVIL TWILIGHT -> The exact moment NIGHT legally begins. Center of sun     |
|                        is 6° below the horizon. (Typically 25-40 min after sunset)|
| NIGHT               -> Center of sun >6° below horizon. Full night flight rules   |
|                        and mandatory green flashing lighting apply!               |
| MORNING CIVIL TWILIGHT-> Sun reaches 6° below horizon before sunrise. Night ends. |
+-----------------------------------------------------------------------------------+

[!IMPORTANT] Sunset vs. End of Evening Civil Twilight: Sunset is NOT the statutory start of night under standard SERA rules. Civil twilight persists for roughly 25 to 45 minutes after official sunset (depending on latitude and season). However, remote pilots must verify national AIPs (Aeronautical Information Publications), as several Member States (such as France or Germany) define night by national decree as commencing exactly 30 minutes after sunset or at official sunset.

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The Mandatory Green Flashing Light Requirement

Under Commission Implementing Regulation (EU) 2019/947, Point UAS.OPEN.060(2)(g), the operational rule governing night flight is unequivocal:

"During flight at night, the remote pilot shall ensure that at least one green flashing light is displayed on the unmanned aircraft."

Concurrently, Commission Delegated Regulation (EU) 2019/945 mandates that all C-class drones intended for Open category operations (specifically Classes C1, C2, and C3) manufactured for the EU market must be equipped with lights that:

1. Allow the unmanned aircraft to be visible in the sky at night.
2. Include at least one green flashing light designed to facilitate aircraft visibility from the ground and distinguish the drone from manned aircraft.

+-----------------------------------------------------------------------------------+
|                 PURPOSE OF THE GREEN FLASHING BEACON                              |
+-----------------------------------------------------------------------------------+
| 1. OPERATOR TRACKING    -> Enables the remote pilot and observers on the ground to|
|                            track the spatial position and movement of the drone.  |
| 2. MANNED AIRCRAFT VIEW -> Warns low-flying manned aircraft (police, air rescue,  |
|                            military helicopters) of an airborne object.           |
| 3. AIRSPACE SEGREGATION -> Distinctly informs pilots and observers that the object|
|                            is an UNMANNED AIRCRAFT, not a distant airplane.       |
+-----------------------------------------------------------------------------------+

Retrofitting Legacy and C0 Drones for Night Flight

• Privately built drones, legacy unclassed drones, and Class C0 aircraft do not always come with a factory-installed green flashing strobe.
• If a remote pilot intends to fly a C0 or legacy drone at night, they must install an aftermarket green flashing strobe (such as a lightweight standalone adhesive LED strobe with an independent battery) prior to takeoff.
• Flying at night without an active green flashing light is a direct statutory violation of Point UAS.OPEN.060(2)(g), subjecting the pilot to immediate administrative fines and license suspension.

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Drone Lighting vs. Manned Aviation Navigation Light Conventions

Understanding traditional aviation lighting standards is crucial for remote pilots to avoid confusing other airspace users and to interpret the lights of approaching manned aircraft.

Under ICAO Annex 2 and SERA Part 3, all civil and military manned aircraft follow an internationally standardized lighting protocol:

• Port (Left Wingtip): Steady RED light (visible through an unbroken arc of 110° from dead ahead to the left).
• Starboard (Right Wingtip): Steady GREEN light (visible through an unbroken arc of 110° from dead ahead to the right).
• Aft / Empennage (Tail): Steady WHITE light (visible through an unbroken arc of 140° facing directly rearward).
• Anti-Collision Beacons: Flashing red beacon on fuselage top/bottom and high-intensity white flashing strobes on wingtips.

+-----------------------------------------------------------------------------------+
|              MANNED AIRCRAFT NAVIGATION LIGHT SECTORS (ICAO / SERA)               |
+-----------------------------------------------------------------------------------+
|                                     0° (NOSE)                                     |
|                                         ▲                                         |
|                                         │                                         |
|                   RED LIGHT             │             GREEN LIGHT                 |
|                   (PORT / LEFT)         │             (STARBOARD / RIGHT)         |
|                   Arc: 0° to 110°       │             Arc: 0° to 110°             |
|                                   \     │     /                                   |
|                                    \    │    /                                    |
|                                     \   │   /                                     |
|              ───────────────────────────┼───────────────────────────              |
|                                         │                                         |
|                                         │                                         |
|                                    WHITE LIGHT                                    |
|                                    (TAIL / AFT)                                   |
|                                   Arc: 110° to 250° (140° total)                  |
|                                         │                                         |
|                                     180° (AFT)                                    |
+-----------------------------------------------------------------------------------+

Why Drones Must Not Mimic Manned Navigation Lights

If a drone were equipped with standard red (left) and green (right) wingtip lights:

• A manned helicopter pilot spotting a tiny red and green light at 100 metres might assume it is a full-sized Cessna or business jet kilometres away, severely misjudging distance and closing speed.
• A remote pilot viewing the drone from underneath can easily misinterpret red and green LEDs when the aircraft rotates, leading to control inversion.
• By mandating a single, distinct GREEN FLASHING light, EASA guarantees that any pilot or air traffic spotter seeing a green strobe immediately recognizes: "This is an unmanned aircraft system."

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Operational Challenges & Human Physiological Illusions at Night

Night flying alters human visual physiology. Remote pilots must recognize the psychological and sensory illusions that degrade spatial awareness in darkness:

1. The Total Loss of Visual Depth Perception

Human depth perception relies primarily on binocular stereopsis (effective only up to ~6 metres) and monocular cues (relative size, linear perspective, atmospheric haze, interposition, and texture gradient). In darkness, all monocular cues vanish. A light 50 metres away looks identical to a brighter light 200 metres away. Judging whether a drone is climbing or descending against an unlit black sky becomes impossible without referencing digital telemetry.

2. The Invisibility of Thin Obstacles

Unlit obstacles represent fatal collision risks at night:

• Overhead High-Voltage Power Lines: Power cables and guy wires do not emit light and reflect zero ambient light against a black sky. They are 100% invisible to the naked eye and to onboard optical vision systems.
• Bare Tree Branches and Crane Jibs: Construction cranes without working aviation obstruction beacons and dormant tree limbs cannot be resolved until impact.
• Unlit Antennas and Guy Wires: Radio towers under 100 metres often lack mandatory aviation warning beacons, forming invisible steel webs in rural and suburban areas.

3. Spatial Disorientation and Visual Illusions

• Autokinesis (The Autokinetic Illusion):
  • Mechanism: When a human stares fixatedly at a single, stationary point of light in a pitch-black, featureless environment for more than 8 to 10 seconds, the eye's involuntary saccadic micro-movements trick the brain into perceiving that the light is moving erratically.
  • Risk: A remote pilot staring at a hovering drone at night may believe the aircraft is drifting uncontrollably to the left or right, prompting unnecessary and erratic stick inputs that can crash an otherwise stable aircraft.
  • Countermeasure: Never stare fixatedly at the drone's beacon. Continuously scan back and forth across the sky, shifting gaze to the remote controller telemetry and surrounding horizon references every few seconds.
• The Black-Hole Illusion During Landing:
  • Mechanism: Occurs when descending over unlit terrain or dark water toward an illuminated landing pad with no surrounding peripheral visual cues.
  • Risk: The pilot misjudges the rate of descent and glideslope, believing the aircraft is higher than it actually is, resulting in a premature high-velocity ground impact.
• Flashlight Glare and Destruction of Dark Adaptation:
  • Mechanism: Human night vision relies on scotopic vision mediated by rod photoreceptor cells containing the photopigment rhodopsin. Full dark adaptation takes 20 to 30 minutes.
  • Risk: Turning on a bright white flashlight or looking at an unshielded smartphone screen instantly bleaches rhodopsin, destroying dark adaptation in a fraction of a second and blinding the pilot for the next 15 to 20 minutes.
  • Countermeasure: Use a dim red flashlight (red light does not degrade rhodopsin) for inspecting equipment and reading checklists. Dim the ground station controller screen to its minimum readable brightness.

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Night Pre-Flight SOP: Inspection & Site Preparation

Operating safely at night demands standard operating procedures executed well before the sun goes down:

+-----------------------------------------------------------------------------------+
|                     STANDARD NIGHT OPERATIONAL FLIGHT WORKFLOW                    |
+-----------------------------------------------------------------------------------+
| 1. DAYLIGHT RECONNAISSANCE -> Inspect the flight area during daylight hours.      |
|                               Identify all trees, wires, cranes, and antennas.    |
| 2. ILLUMINATE THE TOLA     -> Set up LED perimeter ground markers or downward      |
|                               ground lighting on the primary landing pad.         |
| 3. AIRFRAME CHECK          -> Conduct full physical checklist using red/diffuse   |
|                               lighting; confirm green flashing beacon is mounted. |
| 4. CALIBRATE FAILSAFE      -> Set RTH altitude conservatively high (>15 m above   |
|                               the tallest obstacle mapped during daylight).       |
| 5. DESIGNATE BACKUP SITE   -> Pre-illuminate or identify a clear secondary site.   |
| 6. DIM CONTROLLER DISPLAY  -> Reduce tablet brightness to prevent pupil constriction|
+-----------------------------------------------------------------------------------+

1. Mandatory Daylight Site Survey

A remote pilot should never conduct an operation in an unfamiliar area at night without first conducting a thorough daytime site survey. Walking the site during daylight reveals overhead wires, dormant tree canopies, telephone lines, construction cranes, and unpaved terrain that become completely invisible after twilight.

2. Take-Off and Landing Area (TOLA) Illumination

• The launch and recovery pad must be clearly marked and illuminated. Portable battery-powered LED ground pucks or light cones placed at the four corners of the landing zone create a distinct physical landing target.
• Ground illumination must be directed downward onto the landing pad, never pointed upward into the eyes of the remote pilot or the downward optical sensors of the drone.
• The remote pilot must ensure the designated alternate / emergency landing area is equally free of obstructions and identifiable in the dark.

3. Setting a Conservative RTH Failsafe Altitude

During daytime, an automated Return-to-Home failsafe flight allows the pilot to visually monitor obstacle clearance as the drone navigates. At night, unlit obstacles cannot be seen, and optical collision avoidance sensors are inoperative due to low ambient light.

• Therefore, the RTH altitude for a night flight must be configured higher and more conservatively than for daytime operations—comfortably clearing the highest surveyed obstacle within the entire geographical area plus at least a 20-metre safety margin (while never exceeding the 120-metre legal ceiling).

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Practical Flight Scenarios: Night Operations in Practice

+-----------------------------------------------------------------------------------+
| SCENARIO 1: Filming a City Hall Light Projection Festival                         |
| A certified remote pilot is hired to capture aerial video of an illuminated public|
| monument at 22:00 in November.                                                    |
| - Pre-Flight Check: The pilot fits an independent high-output green flashing LED  |
|   beacon to the upper airframe of their C1 drone.                                 |
| - Environment Survey: Conducted during the afternoon; confirmed that no overhead  |
|   tram wires or festival banner cables cross the flight corridor.                 |
| - Visual Ergonomics: The pilot uses a red headlamp while checking propeller nuts  |
|   and dims the tablet monitor to 20% brightness to preserve night vision. The TOLA|
|   is marked with four low-intensity green LED ground markers.                      |
+-----------------------------------------------------------------------------------+
| SCENARIO 2: Thermal Inspection of an Industrial Solar Array at Dusk               |
| An inspection drone flies across an unlit agricultural solar farm 40 minutes after|
| sunset (during astronomical night).                                               |
| - Regulatory Mandate: The pilot ensures the green flashing light is pulsing.      |
| - Hazard Encountered: The pilot experiences the autokinetic illusion while staring|
|   at the hovering drone against the black sky, perceiving that the drone is drifting|
|   toward nearby high-voltage pylons.                                              |
| - Corrective Action: The pilot checks the digital telemetry display, verifies that|
|   ground speed is 0.0 m/s and GNSS hold is rock-solid, looks away to re-orient gaze|
|   against ground horizon lights, and breaks the sensory illusion without making   |
|   erratic manual control inputs.                                                  |
+-----------------------------------------------------------------------------------+

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Common Exam Traps & Pitfalls

• Trap: Green Flashing Light is Optional if Drone Has White LEDs: Exam questions often state: "The drone has bright white forward LEDs and red rear LEDs; is an additional green flashing light needed for night flight?" The answer is YES. Regulation (EU) 2019/947 explicitly mandates at least one green flashing light for night flights. White or red steady lights do not satisfy this legal requirement.
• Trap: Night Begins Exactly at Sunset Under SERA: While everyday language equates night with sunset, SERA strictly defines night as beginning at the end of evening civil twilight (when the sun is 6° below the horizon), unless a specific national aviation decree establishes an alternate threshold (such as 30 minutes post-sunset).
• Trap: Using White Searchlights to Illuminate the Pilot: Spotlights pointed at or near the pilot destroy dark adaptation instantly. All ground lighting must be shielded and directed onto the touchdown surface.
• Trap: Relying on Optical Obstacle Avoidance at Night: Optical flow sensors and stereoscopic vision systems require ambient light to detect textures and surfaces. In the dark, obstacle avoidance systems automatically disable or fail to detect dark obstacles. A pilot must never rely on automated sensors to avoid wires or trees at night.