Understanding VLOS, EVLOS, and BVLOS

Drone VLOS, EVLOS, and BVLOS Terms Explained

Whether you are a novice drone pilot just starting your journey, or a seasoned professional with hours of flight time under your belt, one thing that ties all drone enthusiasts together is the lingo we use – a special language that connects us all in this exciting world of unmanned flight.

You’ve likely come across terms such as VLOS, EVLOS, and BVLOS, whether on drone forums, in user manuals, or in regulatory documents.

But have you ever stopped to delve deeper into what these acronyms actually mean and why they are so fundamental in the realm of drone operation?

Drone VLOS, EVLOS, and BVLOS Terms Explained

VLOS, EVLOS, and BVLOS are acronyms that represent different types of drone flight operations based on the visual line of sight between the drone and the operator or observer. Understanding these terms is essential for safe drone operations and compliance with regulations.


VLOS Visual Line of Sight

VLOS refers to drone operations where the pilot maintains continuous, unaided visual contact with the drone throughout the flight. The pilot must be able to see the drone and the surrounding airspace at all times to avoid collisions and monitor the flight path.

EVLOS – Extended Visual Line of Sight

EVLOS refers to drones flown beyond the visual line of sight of the pilot by using one or more trained observers. These observers maintain visual contact with the drone and communicate with the drone operator about observations and alerts as necessary. This extends the operational radius of the drone but requires more manpower and logistical effort.

BVLOS – Beyond Visual Line of Sight

BVLOS refers to drone operations where the drone is flown out of the visual range of the pilot or observer. This type of operation enables drones to cover far greater distances and has numerous applications, such as infrastructure inventory, monitoring large areas, and creating orthophoto maps. BVLOS operations can provide more data, be more cost-effective, and potentially safer than VLOS or EVLOS operations, depending on the specific use case.

Understanding these terms is not only crucial for maintaining compliance with regulations, but it also can significantly impact the safety, control, and overall success of your drone operations.

CAP 722 Defining Drone Line Of Sight

CAP 722 is a vital document that plays an instrumental role in the world of unmanned aircraft systems in the UK. Think of it as the rulebook that guides how these systems operate. It’s published by the UK’s Civil Aviation Authority (CAA) and provides guidance and policy for operating unmanned aircraft, which includes the drones we love to fly.

It’s a key resource for anyone involved in developing or operating unmanned aircraft systems (UAS) in the UK.

But what exactly does it cover?

CAP 722 helps define important terms and rules that drone enthusiasts and professionals need to follow. Among these definitions are three critical terms for drone operators: VLOS, EVLOS, and BVLOS. These acronyms might seem like a jumble of letters at first, but they’re actually very important for understanding how and where we can fly drones legally and safely.

CAP 722 not only defines these terms but also provides guidelines on how to operate within these parameters. These guidelines are like the lines on a road, helping us navigate the sky, avoid mishaps, and stay within the legal limits set by the CAA.

VLOS – Visual Line of Sight

When you’re flying a drone using Visual Line of Sight (VLOS), you, as the person controlling the drone (the remote pilot), need to be able to see the drone (Unmanned Aircraft or UA) at all times during the flight.

Why is this important?

drone visual line of sight example

When you can see the drone, it helps you control it correctly. Keeping visual contact with the drone allows the drone pilot flying it to always keep an eye on its position, direction, and the space around it. This is necessary to make sure the drone can be moved away from anything that could cause an accident.

‘a type of UAS 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 and
obstacles for the purpose of avoiding collisions.’

A VLOS Operation as defined within UK Regulation (EU) 2019/947

Now, how far away you can be from the drone while still being able to see and control it can change. It depends on a bunch of different things.

It is the responsibility of the pilot to carefully consider all these factors and determine the farthest distance they can safely maintain visual contact with the drone without any assistance.

VLOS Operating Heights Explained

The Open Category of drone operations in the UK is designed for activities that pose a relatively low risk. The Open Category is used for most casual or recreational drone flying, as well as for commercial activities that don’t pose a lot of risks, like aerial photography or inspections of buildings.

Visual Line Of Sight VLOS Drone Height
Source: CAA Cap722

Drones in this category are generally limited to flying no more than 400 feet (or 120 meters) away from the closest point of the earth’s surface. This isn’t just about how high the drone can fly – think of it as if you are tying a 400-foot rope to the drone.

No matter which direction the drone goes, the rope can’t be more than 400 feet away from the ground.

Now, there are a couple of exceptions to this rule:

  1. The first exception is if there’s a tall structure, like a skyscraper or a tower. If the structure is taller than 105m (which is roughly the same as a 30-story building), the drone can fly up to 15m above the top of that structure. But, there’s a catch. The drone must stay within 50m of the structure. This is like the drone is attached to the structure with a 50m leash.
  2. The second exception is for a specific type of drone called an unmanned sailplane. These are usually lightweight gliders. As long as it weighs less than 10kg, it can fly higher than 120m from the earth’s surface, but it can’t be more than 120m above the person who is controlling it.

The main reason for these height limits is to avoid collisions with manned aircraft. Most planes and helicopters fly higher than these limits, but there can be exceptions, so these rules help keep the airspace safe.

VLOS operations at night

VLOS operations at night

There aren’t any specific rules in the UK that stop you from flying a drone at night as long as you can still see it and everything around it. However, if you’re planning to fly a drone at night and you want to get official permission, or what they call ‘operational authorisations’, there are a few more things you need to think about.

The officials will expect you to include a ‘night operations’ section in your operations manual, which is a document where you explain all the procedures you’ll follow when you’re flying your drone.

This should cover:

  1. Daylight reconnaissance and site safety assessment of the surrounding area – This means you should visit the area where you’ll fly your drone during the daytime first. Check it out and make sure it’s safe for your planned flight.
  2. Identification and recording of any hazards, restrictions, and obstacles – While you’re checking the area, make note of any potential risks, such as tall buildings or trees, power lines, or areas where you’re not allowed to fly.
  3. Illumination of the launch site – Your launch site, or the place where your drone will take off, needs to be well lit. This is so you can see clearly when you’re getting your drone ready to fly.
  4. Aircraft lighting/illumination requirements – Your drone needs to have lights on it so you can see it clearly when it’s flying. This might be built-in lights, or you might need to add something to your drone.
  5. Weather limitations for operation – The weather can affect your drone’s flight, especially at night. You need to think about what weather conditions might make your flight unsafe, such as rain, wind, or fog.

So, while there aren’t specific rules against flying a drone at night, you do need to take extra steps to ensure safety and potentially get the required permissions.

Using Aids To Extend Visual Line Of Sight

Using Aids To Extend Visual Line Of Sight

When flying a drone, seeing it clearly is important.

If you normally wear glasses or contacts to see better, that’s fine. You can wear them when you’re flying your drone.

This makes sense, right?

If you need glasses to see clearly in your everyday life, you should also use them to see your drone clearly when it’s up in the sky. But, the rule says you can’t use other tools that help you see things from far away, like binoculars or telescopes.

This also includes any devices that make images appear larger or clearer. The reason behind this rule is simple: if you need these tools to see your drone, it probably means your drone is too far away from you.

Using binoculars might seem like a good idea to some people because binoculars help you see objects that are far away more clearly. When flying a drone, especially one that can go quite a distance, you might think that binoculars could help them keep a better eye on their drone when it’s far away.

However, it’s important to remember that the rules don’t allow the use of binoculars when flying a drone. This is because the drone might be too far away to see any obstacles or other aircraft in its path clearly, increasing the risk of an accident.

Flying your drone too far could be dangerous because you might not be able to see other aircraft or obstacles that your drone could hit.

Hence, always keeping the drone within visible line of sight without enhancement tools (except corrective lenses like glasses or contacts) is key to ensuring a safe flight.

Extended Visual Line Of Sight (EVLOS)

Extended Visual Line of Sight (EVLOS) is a way of flying drones that sits in between normal operations, where the pilot can see the drone directly, and Beyond Visual Line of Sight (BVLOS) operations, where the drone flies out of the pilot’s direct view.

Extended Visual Line Of Sight (EVLOS)

In EVLOS operations, the person controlling the drone might not be able to see it directly all the time, but there are still ways to keep an eye on it and avoid collisions. This is done without the need for high-tech solutions, like special sensors or software.

For instance, you could have extra people helping out who can see the drone when the pilot can’t, known as “observers” or “Spotters”. These observers stay in contact with the drone pilot and let them know if the drone is getting too close to something so that a collision can be avoided.

EVLOS Drone Rules

Normally, EVLOS operations have to fall under a specific set of rules, known as the “Specific category”. However, there are two exceptions to this mentioned in the regulations.

If you want to fly a drone using EVLOS, you have to get permission from the UK Civil Aviation Authority (CAA), the organisation that oversees aviation in the UK. They give this permission in the form of something called an “operational authorisation.” But before they give you this authorization, they look at several things based on a risk assessment.

Here’s what they consider:

  1. Collision Avoidance Procedures: They want to know how you plan to avoid crashing into things.
  2. Drone Size: They’ll look at how big your drone is because larger drones can be easier to see, but they might also cause more damage if they crash.
  3. Drone Colour and Markings: They’ll look at the colour of your drone and any special markings on it. Certain colours and patterns can make your drone easier to spot in the sky.
  4. Additional Observation Aids: If you’re using anything else to help you see the drone or the area around it, they’ll take that into account.
  5. Weather and Visibility Conditions: They’ll consider how clear the weather is and whether there are any clouds in the sky. Both can impact how easy it is to see your drone.
  6. Use of Observers: If you’re using observers to help you keep track of the drone, they’ll look at how you communicate with them.
  7. Operating Range Limits: They’ll want to know that your drone’s radio equipment can maintain control of the drone at all times, especially at the farthest distance you plan to fly.

So, to fly EVLOS, you need to get approval from the CAA and they’ll look at all these factors before they decide to give you permission.

Role Of Observers In EVLOS Drone Operations

Think of the observer as a helper for the drone pilot. This helper keeps their eyes on the drone, especially when it’s too far for the pilot to see. The observer’s position or where they stand is very important. They should be placed where they can clearly see the drone and the space around it.

For Example:

Suppose a drone is flying in a straight line over a long distance, almost like it’s following a road. The pilot might start at the beginning of the ‘road’, and the observer might stand somewhere in the ‘middle’. As the drone flies from the pilot towards the observer, the observer helps the pilot by watching the drone when it gets too far for the pilot to see.

The observer is like an extra set of eyes for the pilot, allowing the drone to fly safely further than the pilot could see on their own. The observer can tell the pilot if the drone is getting too close to something or if there are other risks.

To make this work, it’s really important that the observer and pilot can talk to each other easily and quickly, so they can share information about where the drone is and what’s happening around it.

Beyond visual line of sight operations (BVLOS)

Beyond Visual Line of Sight, or BVLOS for short, is when you fly a drone farther than you can see. This is when a drone is flown beyond the point where the person controlling it (the remote pilot) can directly see it and react to or avoid other things in the air, like planes or birds.

beyond visual line of sight with drone out of view

Because of this, these operations need certain solutions to ensure safety:

  1. Detect and Avoid (DAA) Capability: This means using some sort of technology that can help the drone spot and avoid other objects in the sky, just like a pilot in a manned aircraft would do. This could be done through onboard sensors or software, for instance. Any such technology has to meet specific standards set by both European and UK laws to ensure it’s reliable and safe.
  2. Operational Mitigation: This is a fancy term for any actions or strategies that reduce the chances of your drone running into another aircraft. One common way to do this is through ‘airspace segregation’, which means setting aside specific parts of the sky for your drone to fly in where there are no other aircraft.

However, it’s important to note that the Civil Aviation Authority (CAA), the UK’s aviation regulator, currently prefers the use of airspace segregation over relying on past traffic data for safety reasons when conducting BVLOS operations without a technical DAA capability.

So, in simple terms, if you want to fly a drone far enough that you can’t see it, you need to have a plan for how to avoid other things in the sky. This could be through technology that lets the drone detect and avoid other objects, or by choosing a part of the sky to fly in where you’re not likely to encounter other aircraft.

How To Conduct BVLOS Drone Flights

The main way to do drone operations where the drone flies beyond what you can see (BVLOS operations) without using special detect-and-avoid technology (DAA) is through something called “airspace segregation“. This basically means that you dedicate a specific chunk of sky just for your drone to fly in, where there won’t be any other aircraft. It’s like drawing an invisible “safe zone” in the sky for your drone.

Now, some people might argue that it’s safe to fly a drone based on past data about where other aircraft have flown. This is called a “probabilistic safety argument“. Think of it like looking at where cars have driven on a road in the past to decide where it’s safe to skateboard.

However, the Civil Aviation Authority (CAA) – that’s the UK’s air traffic control organisation – doesn’t currently agree with this method.

They don’t believe that relying solely on past data about where other aircraft have flown is enough to guarantee safety when flying a drone beyond what you can see. They want more concrete safety measures in place, like the aforementioned airspace segregation or the detect-and-avoid technology.


In conclusion, navigating the world of drone operation can be a complex task, given the different operational concepts like VLOS, EVLOS, and BVLOS. It’s crucial to understand these terms and the regulations around them to ensure safe and legal drone operations.

Visual Line of Sight (VLOS) operations are the simplest, where the pilot must always have the drone in sight. Extended Visual Line of Sight (EVLOS) adds a layer of complexity by allowing the use of additional observers to maintain visual contact with the drone when the pilot can’t directly see it. Beyond Visual Line of Sight (BVLOS) is the most complex and requires specific permissions due to the added risks involved, needing either technology to detect and avoid obstacles or strategies to segregate the drone’s airspace from other aircraft.

Each method of operation comes with its own set of rules and guidelines, all designed to ensure the safety of all airspace users. As the technology evolves and regulations continue to adapt, understanding these terms will be increasingly important for anyone involved in drone operations.

As we move forward into an era where drones become more integrated into our everyday lives, let’s do so with safety, responsibility, and respect for the laws and guidelines that govern our shared airspace.

Leave a Comment

Your email address will not be published. Required fields are marked *