How to Fly Your Drone Safely near People or ProperTy

2021-06-07 21:15

In Canada and the USA and most other jurisdictions (the European Union being the only big exclusion), small drones, more formally known as Small Remotely Piloted Aircraft Systems (sRPA/sRPAS) (which are defined as any RPA/RPAS weighing at least 250 grams), must be registered, and flying them requires a pilot certificate. You must also follow strict rules when flying a sRPA/sRPAS.

That's why the market has been innundated with "Micro-drones" aka Micro RPA/RPAS or Micro UA/UAS, which are drones weighing 249 grams and below. The mRPA/mRPAS and mUA/mUAS acronyms are also becoming more prevalent to refer to these types of drones. Micro-drones are designed to allow civilian drone owners to operate drones without needing to get a pilot certificate or to register their drones, both of which the new regulations now require for sRPA/sRPAS and above. Simply said, pilots of micro-drones are not bound by the same requirements as other drones.

While there are no prescriptive elements of the regulations, there is an expectation that the pilot of a micro-drone use good judgment, identify potential hazards, and take all necessary steps to avoid any risks associated with flying your drone.

So does that mean you can fly your micro-drone safely near people or property? What about small drones in general?

How CloSe to People or ProperTy can I fly my drone?

Regardless of whether you're flying a small drone (weighing between 250 grams and 25 kg) or a micro-drone (weighing 249 grams and below) near people or property, the safety considerations should be the same. However, governments have admitted that the heavier the drone, the higher the risks, and therefore the applicable rules are generally more restrictive for heavier drones.

First off, it's important to specify that if you're operating any drone, you must follow the rules in your jurisdiction, which generally means you need to ensure it is registered, you must obtain a pilot certificate, and you must also follow strict rules when flying your drone. The rules might outright prevent you from operating your drone over or near people or property or in specific locations, or even require you to obtain special certification. Sometimes you also need to get permission before flying (like when you're flying in certain airspace or locations). Refer to my previous blog post about how to become a drone pilot to learn more about the basic rules (like the altitude limit of 400 ft AGL or the VLOS rule).

Rules are rules, and everyone must follow them. Failure to follow them will lead to fines (in Canada, you can be fined up to $3,000 for putting people at risk).

For example, in Canada, when flying a small drone under a pilot certificate — small remotely piloted aircraft (VLOS) — basic operations, you are not allowed to fly at a distance of less than 100 feet (30 m) from another person, measured horizontally and at any altitude, except if that person is a crew member or other person involved in the operation. In simpler terms, you're not allowed to fly 'near people' or 'over people'.

Even with a pilot certificate — small remotely piloted aircraft (VLOS) — advanced operations , in Canada you can only fly 'near people' or 'over people' using small drones that have been certified for such operation (generally by TCCA working with the manufacturer) and whose certificate of registration explicitly specifies it. Additional requirements also apply.

However, strictly speaking, the only aviation regulations that apply to micro-drones in Canada is Canadian Aviation Regulation (CAR) Part IX paragraph 900.06 which states that "No person shall operate a remotely piloted aircraft system in such a reckless or negligent manner as to endanger or be likely to endanger aviation safety or the safety of any person. ". Of course, other laws apply as well (e.g. Privacy Act).

There's a similar situation in the USA, where 14 CFR Part 107 certified remote pilots of small drones require a waiver to operate near or over people, but those rules don't strictly apply to micro-drones. In fact, if you want to fly any small drone (below 55 pounds) for purely recreational purposes, there is a limited statutory exception ("carve out") (USC 44809) that provides a basic set of requirements.

So before you venture to operate your small drone or micro-drone near people or property, the first step is to make sure you're very familiar with the regulations in your jurisdiction.

In a separate blog post on how to become a drone pilot, I also advise people to use sound judgement when making the decision to fly your micro-drone where the regulations would otherwise prohibit you from flying a small drone. I also list guidelines to avoid flying in a negligent or reckless manner and being subject to fines. Remember: if you feel that your flight is risky, don’t do it.

So with all of that said, lots of people in Canada and the USA ask whether they can operate their micro-drones safely near people, or property for that matter...

So let's say you're a micro-drone pilot and you're very tempted to fly your micro-drone during an outdoor concert so that you can get epic aerial videos, and you might justify it to yourself by thinking "it's so small, and the regulations don't strictly prevent me from flying it". That's the wrong attitude...

I recommend that micro-drone pilots adopt the following approach whenever you want to fly your micro-drone and the regulations would prevent you from operating that flight should you have operated that flight with a small drone instead of a micro-drone: perform a safety assessment and use that as a basis for deciding if it's safe to fly or not, and if so set clear limitations for your flight to mitigate the risks as much as practical.

Small drone pilots should also adopt the same approach. In fact, when Transport Canada Civil Aviation (TCCA) certifies certain small drone models for Advanced operations, they do so based on RPAS Safety Assurance declaration submitted by the drone manufacturer which is based on an aircraft and system safety assessment approach. In Europe, small drone operations under the 'specific' category actually require operators to take into account the mitigation measures identified in an operational risk assessment (what I call a safety assessment), except for certain standard scenarios where a declaration by the operator is sufficient.

In fact, all drone pilots should follow this advice, really... The operation of bigger drones (which carry higher risk when operating near people, property, or other aircraft) are much more constrained and regulated; they are usually built for specific missions and flight profiles, and generally don't get as close to people as micro-drones or small drones do. For those bigger drones, the regulatory authorities and drone manufacturers are the ones who perform the safety assessment which allows them to create specific operating procedures and limitations that drone operators must follow in order for the drone to be operated safely. So as long as you follow the manufacturer's manuals, you should be able to safely operate bigger drones. For small drones, it's a bit the same, although pilots must be certified and must follow clear rules which ensure a minimum level of safety. For micro-drones, while the manufacturer's documentation might contain specific operating procedures and limitations that pilots must respect, the pilots themselves have a bigger role to play since they are not bound by any specific rules or sets of procedures or limitations, and pilots have a certain leeway to put their own specific operating procedures and limitations in place since smaller weight drones pose less of a risk to people, property, and other aircraft.

So it's even more important to perform a safety assessment before flying a micro-drone near people or property. Nobody else has performed one for you! Furthermore, the flight parameters can be even more varied when it comes to micro-drone flights because they are much more versatile and can operate from all kinds of places, therefore each safety assessment might have a different outcome. Don't become complacent, and if you haven't followed this advice before, please avoid flying the same risk again just because you didn't get in trouble last time you did it. This is a sure way of getting yourself into trouble the next time... And by getting into trouble, you get us all into trouble on the long run.

How to perform a Safety Assessment (or Operational Risk Assessment) and Identify Mitigation Measures?

The way you perform a safety assessment is complex, and I suggest you do some separate reading on it (SAE ARP4761 is a good reference, but the European Union regulations also cover it well), but the simple approach is to:

  1. Identify all possible failure scenarios.

  2. For each failure scenario, assign a hazard severity and a probability of occurrence. You can use a fault-tree analysis approach to combine multiple independent failures and probabilities to reach the top event.

  3. Use a risk matrix to decide if the risk is acceptable or unacceptable.

  4. If the risk is acceptable, no further mitigation measures are required for that particular flight. If the risk is unacceptable, conceive possible mitigation measures to reduce the hazard severity or probability of occurrence for the failure scenarios that are driving the unacceptable risk. If the risk becomes acceptable, ensure all the necessary mitigation measures (and any associated limitations) are put in place for that particular flight.

Once you've performed a safety assessment for one such flight, many of the failure scenarios and association mitigation measures can be re-used in subsequent flights as well if they apply, as long as they are adequately reviewed and revised to factor in the specific flight, location/site and environmental parameters for that subsequent flight.

Keep in mind the main risks of any drone flight are the risk of serious injury to people or damage to property because of:

  1. High speed rotating parts (e.g. propellors)

  2. The kinetic energy of the drone itself, while in controlled or uncontrolled powered flight

  3. The potential energy of the drone itself while it's hovering at altitude. If it "falls out of the sky" due to a failure, malfunction, or defect, that potential energy will quickly transform itself to kinetic energy (damn gravity!).

These are not the only risks (disruption to airspace is another risk, and so is the risk of collision with another aircraft, so do make sure to cover related failure scenarios in your safety assessment), and note that you also need to consider the combination of these 3 things. For example, you might have one or more motors fail and your micro-drone might spiral out of control and crash into a crowd at high speed with some of the propellers rotating at high speed! Keep in mind that even 249 grams travelling at 13 m/s (which happens to be the maximum speed of my Mavic Mini in 'S-mode') caries quite a bit of energy and can do quite a bit of damage and cause serious injuries.

Furthermore, you need to respect other factors (e.g. like people's privacy) which might be more difficult when you're flying near lots of people and buildings.

Here are some good way of mitigating the risk should you decide to perform the flight after performing your safety assessment:

  • Have your friends act as flight crew members and/or visual observers, to keep curious people away from your micro-drone, especially the take-off and landing zone, and help you detect any obstacles or dangers.

  • Set a limit for how close you want to get to people:

    • if performing a micro-drone flight within 100ft of people, limit that flight to only using slow speed modes. On my Mavic Mini, I limit myself to only using 'P-mode' or 'C-mode' for flights within 100ft of people, and just 'C-mode' whenever I'm flying closer than 30 ft from people (In 'C-Mode', the maximum flight speed is limited to 4 m/s, maximum ascent speed is limited to 1.5 m/s, and maximum descent speed is limited to 1 m/ s, so ).

    • if performing a micro-drone flight over people (I don't like to do this, as a general rule, but sometimes it can be done safely if proper mitigation measures are in place):

      • use the prop guards or protective safety cage to mitigate the risk from the high speed rotating props should the micro-drone experience a failure/malfunction and crash into people or property.

      • Set a lower max altitude for your flight (my Mavic Mini has a specific setting for this). Pick a max altitude which is high enough to keep your as far away as possible from people (e.g. more than 100 ft if you can) and low enough to minimize the kinetic energy should your drone fall out of the sky due to a failure or malfunction. 150 ft is a good general max altitude I use for these kinds of flights.

  • if performing a drone flight near possible obstacles (e.g. trees), use the prop guards or protective safety cage to mitigate the risk of foreign objects jamming your propellers and sending your drone out of control.

  • put a limitation to ensure you perform the flight following a fresh compass calibration and with all the sensors and augmentations available: GPS, ground-view hover cameras (Downward Vision system sensors), etc...

On the positive side, the DJI Mavic Mini drones (and DJI's drones, in general) have very reliable designs and components and impeccable build quality, therefore the probability of a failure, malfunction, or defect causing death is probably in the order of 'extremely improbable'. However, I prefer not taking any unnecessary risks if they can be avoided. This is also the reason I stay away from imitations and other chinese-made copy-cat drones; they're much less reliable.

One last thing: looking at FAA's trend analysis on Part 107 waiver requests to fly over or near people using small drones, it also gives you a good idea of what the FAA is looking for in successful waiver applications, and you can clearly see that most applicants proposed:

  1. using an experienced pilot

  2. using a reliable aircraft design.

  3. offer mitigation measures to reduce laceration injury (such as parachutes, and/or propeller guards)

  4. offer appropriate limitations (altitude, airspeed, time flown over people, population size and density, geo-fencing, environmental limitations)

Other Considerations for Safe Operation of Your Drone Near People or Property

So you've performed a safety assessment and put in place adequate mitigations, and you're going ahead with your flight near people or property... Great. Now what?

Like pilots who fly any aircraft, it all comes down to airmanship and knowledge. Airmanship can't be thought, but it can be practiced. Knowledge can be thought, if you're willing to learn.

One of the most important parts of safe operation near people or property is knowing your drone's performance and operating characteristics and limitations. This becomes especially important for micro-drones. For example, at maximum flight speed, my Mavic Mini requires a minimum braking distance of 30 m in windless conditions. At maximum descent speed, a minimum braking distance of 10 m is required in windless conditions. Note that 30m is pretty much the 100 ft minimum distance small drones need to keep from people per the regulations, so just because you're following the regulations doesn't mean you're always safe. Knowing this kind of performance information helps keep a mental barrier at which point you need to take evasive action to avoid collisions with people or property. You shouldn't get that close anyhow.

It's also important to have a good handle on your drones' airspeeds to ensure you account for the closure rate to people or property. For my Mavic Mini, the max speed is 46.8 km/h (29 mph) flying in Sports mode at close to sea level with no wind. The speed breaks down as follows for the different flight modes;

  • 13 meters per second (42.65 feet) in S-Mode (Sports)

  • 8 meters per second (26.24 feet) in P-Mode

  • 4 meters per second (13.12 feet) in C-Mode

One important fact which often differentiates micro-drones from bigger drones is that they don't have obstacle detection and collision avoidance features since they don't have the sensing technology built in to detect and avoid obstacles. It's generally too difficult to fit this into such small drones. So you really can't count on these added safety features which are more and more common on newer small drones.

Proper flight planning is even more important when flying your micro-drone near people or property. Prior to flight, check weather conditions. Check if there are any airspace or location restrictions. Get familiar with the site using satellite imagery on Google Maps, or better yet 3D view in Google Earth, so that you can put together a good plan for your flight and stay away from obstacles or dangers (e.g. ridges where wind effects might be more pronounceD).

Another important consideration is proper maintenance and pre-flight inspections and checklists ahead of your flight near people or property. Ensure the drone is well maintained, safe and airworthy before flight (now would be a good time to replace damaged propellers or components). Use fully charged and known-to-be-good batteries. Don't skip a step in your pre-flight inspections and checklists.

Weather and environmental conditions are also an important element. Do not use your mini drone in severe weather conditions such as gusting winds, snow, rain, and fog. Pay particular attention for changes in visibility (presence of fog, cloud ceiling), precipitation (imminent storms, possible icing), temperature & humidity (density altitude effects), and wind speed and direction (pay attention to sudden changes). Remember that environmental factors such as wind and icing might have a bigger effect on a lighter micro-drones than they do on a small drone or bigger drones.

Wind can result in horizontal shifting, which may present hazards especially when flying near people or property. Gusts can also bring unpredictability to the horizontal shifting, and even if your drone's full suite of stabilization sensors are operating (even micro-drones have fancy sensors to stabilize flight; the Mavic Mini uses both Downward Vision system Sensors + GPS signal for precision hovering) they might not be able to cope with gusts of wind, and you might not be able to control your drone and prevent it from flying towards people or property unintentionally. In fact, the DJI Mavic Mini can only handle a maximum wind speed of 8 meter per second (Scale 4, 28km/h or 15.5kts). Furthermore, as the battery level decreases, especially in low-temperature environment, the wind speed resistance also decreases. The drone may not be able to return to a Home Point when the wind speed is too high. Fly with caution. Also plan to fly into the wind if you can, to come back with the wind as the battery strength decreases. Don't forget to signal to crew and bystanders to stand clear for take-off (ensure no one is downwind from the micro-drone in case of take-off drift).

Also note that the hot temperatures or high altitudes reduce your drone's lift performance for the same amount of available power. Consider that your drone won't be capable of its maximum performance under such ambiant atmospheric conditions.

Make sure to use all of the automation and safety features offered in your control station and flight controller software. Set an appropriate maximum altitude (not too high as explained before), a Return-to-Home (RTH) altitude, and a Home Point away from people, so that in the case of remote control signal loss, the Failsafe RTH can be automatically activated and steer the drone away from people and back to your Home Point

It's also useful to memorize your "Fly Away" or "Loss of VLOS" procedure. For example, on the Mavic Mini, upon realizing of potential fly-away (e.g. wind carries drone away, uncommanded movement) or loss of VLOS, I immediately make the aircraft brake by pressing the Flight Pause/RTH button once. If it's being blown away by strong winds, I switch to S-Mode (Sports) and fly back towards myself while descending to the minimum safe altitude (wind speeds decrease with altitude, and closer to the ground).

Lastly, if you lose your drone from your VLOS, don't panic! Often, your drone is flying just fine, and you just weren't paying attention and lost it from view. This might happen if you fly your drone too far and you're inattentive and it gets lost against a cloudy backdrop (micro-drones are very small, after all). Just keep calm and follow your procedures. If you can't manage to fly it back into VLOS, and the automatic return to home functions don't work and if video is still streaming, use video to land in a safe landing area away from people and property. If video is not streaming, attempt to recover VLOS by moving towards the direction where you last had spotted your drone, and once VLOS is re-established control emergency landing as best you can (steer away from people and property). In my limited experience, the control station does a good job to re-establish command and control pretty quickly as long as you're within range.

In the worse case that you've lost control of your drone and it's headed towards people, warn them! This sounds obvious, but I've actually added this step to my checklists so I don't forget. If it's flying towards restricted airspace like an airport, warn air traffic control (if you prepared and performed adequate flight planning ahead of time, you would have written down their telephone number or looked up the ATC communication frequencies).

These are just the basics. The more you read, the better you'll be prepared.

I've personally developed a very thorough set of operating procedures, limitations, and checklists for my Mavic Mini, so don't hesitate to use it as a starting point. It's quite detailed, and it also has a section on camera settings and awesome cinematographical shots. Check it out:

Hagop's Mavic Mini Flight Manual v1.0