Drones and the definition of a Populous Area

CASR 101.025 - Meaning of Populous Area

For this Part, an area is a populous area in relation to the operation of an unmanned aircraft or rocket if the area has a sufficient density of population for some aspect of the operation, or some event that might happen during the operation (in particular, a fault in, or failure of, the aircraft or rocket) to pose an unreasonable risk to the life, safety or property of somebody who is in the area but is not connected with the operation.

What makes an area populated?

As the rule says, it is all based on risk.

We need to evaluate the risk before we fly in order to determine if the area we are flying in is “populated”. This varies greatly depending on the type of RPA you are using.

Imagine a scenario where you are flying a lightweight fixed wing RPA over a small country town, you may possibly be doing a survey or something similar. If your aircraft suddenly loses power, it will continue to glide at a ratio of around 15 to 1 and come to earth well away from the town. So in terms of our risk assessment, provided your altitude is sufficient, the risk of actually crashing in the town is minimal.

However, with the same scenario, using a Quad-rotor like the DJI Inspire, any sort of power failure would cause it to drop like a stone scattering wreckage and litigation all over the place.

So, in general, the higher you are with a fixed wing, the lower the risk to the area beneath it. The higher you fly with a multi-rotor, the greater the risk to the area beneath it.

So what do I have to take into consideration when evaluating the risk to the general population?

Restricting ourselves to Multi-Rotors, there are a number of things we need to consider.

First is the number of rotors. If we are flying a Quad-Rotor (4 propellers), then we have to assume that if any component anywhere in the RPA fails, it will crash. It cannot fly on 3 propellers, so if a motor, propeller, esc or any other component fails, it will crash.

Next is the controller. Controllers fail, there are a number of reasons:

  • Mid-air reset
  • Signal Loss
  • Electronic Component Failure
  • Physical Failure – The IMU chips for some popular controllers have been known to come loose inside the controller unit and cause erratic flight and crashes.
  • Vibration Saturation – Excessive vibration in the airframe can saturate the IMU unit’s inertial sensors and cause the controller to lock up. This usually results in the aircraft flipping and crashing if you don’t notice the indicator LED in time.

GPS units can fail, move or become completely dislodged during flight which can also cause very erratic behaviour – especially if Return to Home is triggered.

In short, the regulation REQUIRES us to assume that a standard quad rotor WILL crash during or flight – a 1 to 1 risk ratio – because we have not taken any measures to mitigate the risk.

So if you are flying a Phantom in the front yard of a house on a normal suburban block, then you are in a populated area. You cannot say with any measurable degree of certainty that the RPA will not suddenly malfunction and crash on the road or footpath or anywhere else close by, as you have not done anything to mitigate the risk.

So how can we mitigate the risks involved?

Firstly, we can use an Octo-Copter (8 propellers), as these can continue to fly in a stable and controllable way if one rotor fails. So this gives us our first degree of risk mitigation.

Next, we can install a dual controller system (there are several good systems on the market, but they are not cheap). Installing a dual controller will normally mean that we will also have dual GPS, introducing another 2 degrees of risk mitigation.

Finally, we can install a parachute. This is usually activated by an excessive rate of decent or radical roll / pitch / yaw movements. This gives us another degree of risk mitigation.

So with an octo-copter with dual controllers, dual GPS and a parachute, we can be confident to say that it is extremely unlikely to crash and that the risk of damage or injury is minimal.

THIS DOES NOT NEGATE IN ANY WAY THE 30 METRE RULE! You must still be at least 30 metres – HORIZONTALLY MEASURED – from any person that is not directly involved with the flight.

There are other ways you can mitigate the risks. For instance, you can tether your drone (literally tie a strong tether to it and secure the other end to the ground). This sounds like a good idea, but you need to bear in mind that the tether will need to prevent the RPA from leaving your controlled area. So if you are in the front yard, the rope must be short enough so that the drone will not reach the footpath. This in turn will limit your altitude to the length of the tether.

Don’t forget that every infringement could cost you $850 and 3 points of your RPC (you only have 12), as well as a separate $850 fine for the UOC holder and 3 points of your UOC.

CASA will have no hesitation in tearing up your RPC and your UOC once you get to 12 points!

You need to understand that CASR 101.025 can be applied retrospectively. So if you have an incident and some injury or damaged occurred and you did not take measures to mitigate the risk, then you were most likely in a “populated” area.

In the end it’s not about the money or the points, it’s about safety.