In simple terms, for every 1 metre high your drone is you must stay 1 metre away from uninvolved people
The 1:1 rule with the A2 CofC
The 1:1 rule is a new addition to UK drone operators and is only applicable to operators flying under the A2 CofC with a C2 drone in low-speed mode OR if you are operating within the A3 Subcategory with any aircraft up to 25 kg.
Although it is only required that you follow the 1:1 rule with a C2 aircraft in low speed made, we always advise using this as a rule of thumb to ensure you can maintain a safe distance from uninvolved people with your aircraft.
The simplest way to describe the rule is that it is a height restriction directly affected by the distance you are away from uninvolved people. For example, starting at ten meters separation from uninvolved people and ten meters above the ground, for every metre you fly closer you must descend one metre.
You can fly lower than the distance you are separated from people, but not higher. This may seem strange, but it does make sense once you get your head around the reasoning behind the rule.
The rule is very specifically written with safety as the primary objective. Most multi-rotor aircraft, especially quadcopters with four motors, cannot sustain flight in the event of a failure - for example, collision with a bird which damages a propeller. When a failure occurs they will almost certainly drop vertically downwards and totally out of control. The 1:1 rule ensures that the drone is always far enough away to clear uninvolved people if the worst were to happen and it dropped out of the air.
We have produced a short animation which illustrates the 1:1 rule in action.