Simulator
Viva-voce
Simulator
Best viewed on tablet, laptop, or desktop. For mobile access, please enable Desktop Mode.
Aim
To study and visualize the operational concepts of Visual Line of Sight (VLOS), Extended Visual Line of Sight (ELOS/EVLOS), and Beyond Visual Line of Sight (BVLOS) in unmanned aerial vehicle (UAV) missions.
Theory
UAV operations are commonly classified according to the level of visual contact maintained between the operator and the drone:
- VLOS (Visual Line of Sight): The pilot must directly see the UAV at all times without technological visual aids beyond standard corrective lenses.
- ELOS / EVLOS (Extended Visual Line of Sight): Additional observers or support systems help extend situational awareness beyond the pilot’s immediate view.
- BVLOS (Beyond Visual Line of Sight): The UAV flies outside direct visual observation and depends on telemetry, navigation systems, communication links, and detect-and-avoid capabilities.
In real UAV operations, buildings, terrain, atmospheric conditions, and distance may limit visual awareness. Therefore, understanding these operational modes is essential for flight safety, regulatory compliance, and mission planning.
Simulation Procedure
- Open the simulation dashboard in a browser.
- Click Show VLOS Demo to observe a drone operating within the pilot’s direct visual range.
- Click Show ELOS Demo to observe how an external observer and escort aircraft help extend operational visibility.
- Click Show City BVLOS Demo to study how urban obstacles block direct line of sight.
- Click Show Far BVLOS Demo to observe long-range UAV operation outside direct human visibility.
- Use Reset to restore the initial condition and repeat the experiment.
The animated lines in the simulation represent communication, visibility, or blocked line-of-sight relationships among the pilot, observer, UAV, and support aircraft.
UAV Visual Line of Sight Simulation
Beyond Visual Line of Sight
Pilot
Visual Line of Sight
Observer
Extended Line of Sight
Escort Crewed Aircraft
Beyond Visual Line of Sight
Initial state. Select a demonstration.
Operational Feature Comparison
| Feature | Who sees the drone? | Visual Aids | Typical Range | Endurance | Operational Range | Best Use Case |
|---|---|---|---|---|---|---|
| VLOS | The Remote Pilot | Corrective lenses only | ~500 metres | 0.3–2 hours | 0–5 km | Training, inspection, hobby |
| EVLOS / ELOS | A Visual Observer | Observers use radio | Extended by observers | 2–10 hours | 5–50 km | Industrial monitoring, corridor tracking |
| BVLOS | No one (instrument-only) | Sensors, GPS, & DAA | Tens of kilometres | 10+ hours | 50+ km | Delivery, surveillance, long-range missions |
Observation
- In VLOS, the UAV remains visible to the pilot, allowing direct situational control.
- In ELOS, an observer extends visibility and supports safer operations over a wider range.
- In City BVLOS, tall structures obstruct direct vision, creating blind zones.
- In Far BVLOS, the UAV cannot be seen by the pilot and must rely on remote systems.
- The simulation demonstrates that increasing distance and physical obstacles reduce direct pilot awareness.
Applications
Drone Training
UAV Regulations
Mission Planning
Defense Surveillance
Remote Inspection
Aviation Safety
This simulation can be used in UAV education, aviation training, defense technology demonstrations, drone certification modules, and interactive classroom learning.
Learning Outcome
After completing this simulation, the learner will be able to:
- Differentiate between VLOS, ELOS/EVLOS, and BVLOS UAV operation modes.
- Explain how visual range affects pilot situational awareness and mission safety.
- Understand the role of observers and support aircraft in extending operational visibility.
- Recognize how buildings and distance can create operational limitations.
- Apply the concept to UAV regulations, mission design, surveillance, and remote operations.
Viva-voce
Best viewed on tablet, laptop, or desktop. For mobile access, please enable Desktop Mode.
Common Q & A
1) What does VLOS mean in UAV operation?
VLOS stands for Visual Line of Sight. It means the drone must remain directly visible to the remote pilot without using binoculars, camera feed, or other visual aids. The pilot should be able to monitor the UAV’s position, direction, altitude, and surrounding airspace at all times.
2) What is EVLOS in UAV operations?
EVLOS means Extended Visual Line of Sight. In this operation, the UAV may fly farther than the pilot’s direct viewing range, but trained visual observers are positioned along the route to maintain visual contact and assist the pilot.
3) What is BVLOS?
BVLOS stands for Beyond Visual Line of Sight. It refers to drone operations where the UAV flies outside the direct visual range of the pilot. Such operations depend on telemetry, navigation systems, communication links, onboard sensors, and automated safety systems.
4) What is an autonomous UAV?
An autonomous UAV is a drone that can perform flight tasks with minimal or no direct human control. It can automatically handle functions such as:
- Takeoff
- Navigation
- Obstacle detection
- Mission execution
- Landing
5) Why is VLOS considered the safest basic mode of UAV operation?
VLOS is considered safer because the pilot can directly observe:
- Drone movement
- Nearby obstacles
- Other aircraft or birds
- Unexpected behavior
6) What is the main difference between VLOS and BVLOS?
The main difference is visibility and dependence on systems:
- VLOS: Pilot directly sees the UAV
- BVLOS: Pilot depends on sensors, telemetry, communication links, and automation
7) What are visual observers in EVLOS operations?
Visual observers are trained personnel who help maintain visual contact with the UAV when the pilot alone cannot see it clearly. They communicate with the pilot regarding:
- Drone position
- Nearby hazards
- Airspace conflicts
- Emergency situations
8) What technologies are important for BVLOS flight?
Important technologies for BVLOS include:
- GPS/GNSS navigation
- Telemetry systems
- Long-range communication links
- Autopilot / flight controller
- Failsafe logic
- Obstacle detection systems
- Return-to-home system
- Redundant power and communication systems
9) What is meant by autonomous navigation in UAVs?
Autonomous navigation means the UAV can move from one point to another without constant manual control by using:
- Waypoints
- GPS data
- IMU sensors
- Obstacle sensors
- Navigation algorithms
10) What is a waypoint mission in UAV operation?
A waypoint mission is a pre-planned flight path where the UAV automatically travels through a series of predefined coordinates. It is commonly used in:
- Surveying
- Mapping
- Agriculture
- Inspection
- Surveillance
11) What is Return-to-Home (RTH) in UAVs?
Return-to-Home (RTH) is a safety feature that commands the UAV to automatically return to its takeoff point or a predefined home point when:
- Battery becomes low
- Signal is lost
- Mission ends
- Failsafe is activated
12) Why are communication links critical in BVLOS operation?
In BVLOS operation, the UAV is not directly visible, so the pilot depends on communication links for:
- Flight control
- Telemetry updates
- Video/data transmission
- Emergency override
13) Can an autonomous UAV fly completely without sensors?
No. An autonomous UAV depends heavily on sensors such as:
- GPS
- Gyroscope
- Accelerometer
- Magnetometer
- Barometer
- Obstacle sensors
14) What are the major applications of BVLOS UAVs?
BVLOS UAVs are widely used in:
- Long-distance inspection
- Powerline and pipeline monitoring
- Large-area surveying
- Agricultural monitoring
- Disaster response
- Logistics and delivery
- Border surveillance
15) What is the major advantage of autonomous UAV systems?
The major advantage is that they can perform missions with:
- Higher repeatability
- Reduced pilot workload
- Improved mission efficiency
- Better route accuracy
- Capability for complex operations
Tricky Questions
1) If a drone is visible only through its onboard camera, is it still VLOS?
No. That is not VLOS. In VLOS, the pilot must see the drone directly with unaided vision. Watching it through FPV or camera feed alone does not qualify as VLOS.
2) Can EVLOS be considered the same as BVLOS?
No. EVLOS and BVLOS are different. In EVLOS, visual contact is still maintained through observers. In BVLOS, the UAV operates completely outside direct visual observation.
3) If GPS fails during autonomous flight, can the UAV still continue?
It depends on the system design. Some UAVs may continue temporarily using:
- IMU
- Compass
- Vision sensors
- Inertial estimation
4) Is an autonomous UAV always fully intelligent like AI?
No. Not all autonomous UAVs use advanced AI. Many autonomous drones simply follow:
- Pre-programmed logic
- Waypoint paths
- Sensor-based feedback control
5) If telemetry is available, is visual observation unnecessary in VLOS?
No. Telemetry is only a supporting tool. In VLOS operation, direct visual monitoring is still necessary regardless of telemetry availability.
6) Can a BVLOS drone operate safely without obstacle detection?
It is highly risky. Since the pilot cannot directly see the drone, BVLOS operation should ideally include:
- Obstacle sensing
- Airspace awareness
- Failsafe routing
- Emergency logic
7) If the UAV follows waypoints correctly, does that mean it is fully autonomous?
Not necessarily. Waypoint following is only one part of autonomy. A fully autonomous UAV should also handle:
- Navigation corrections
- Unexpected obstacles
- Environmental disturbances
- Failsafe decisions
8) What happens if communication is lost during BVLOS operation?
The UAV should enter a failsafe mode. Depending on programming, it may:
- Hover
- Return-to-home
- Land automatically
- Continue mission under predefined logic
9) Can a drone be autonomous and still require a human operator?
Yes. Most real-world autonomous UAVs still require a human operator or supervisor for:
- Mission planning
- Safety monitoring
- Emergency intervention
- Regulatory compliance
10) Is BVLOS always better than VLOS?
No. BVLOS is not always “better”; it is simply suitable for different mission requirements. VLOS is simpler and safer for training, inspection, and short-range missions, while BVLOS is useful for long-range and large-area operations.
Short Viva Tip
If the examiner asks “Explain VLOS, EVLOS, BVLOS, and Autonomous UAV in one line”, you can answer:
“VLOS means the drone remains directly visible to the pilot, EVLOS extends visibility using observers, BVLOS allows operation beyond direct sight using advanced systems, and autonomous UAVs can perform missions with minimal human control.”
Quick Viva Trick:
“VLOS means the drone remains directly visible to the pilot, EVLOS extends visibility using observers, BVLOS allows operation beyond direct sight using advanced systems, and autonomous UAVs can perform missions with minimal human control.”
Quick Viva Trick:
- VLOS = Pilot sees the drone
- EVLOS = Observer helps see the drone
- BVLOS = Systems help control the drone beyond sight
- Autonomous = Drone can think/act based on programming and sensors