Let’s talk about 400ft

The internet loves an argument. 

I’m sure the CAA thought that putting out a notification that from 30th July 2018, the maximum legal height (NOT ALTITUDE) for a drone, hobby or PfCO (not withstanding separate OSC exemptions), was to be 400 of our imperial feet, would be accepted in a straightforward manner.

Oh how wrong they were!

We know the CAA like to mix up measurements, with PfCO maximum distances in decimal meters but nonetheless they have stuck with imperial for height and it is feet.

That’s Above Ground Level (AGL).

This bit has led to some confusion, amongst hobby and commercial users alike in some groups. Interpreting what the ground is has proven tricky.
The simple explanation is the weighted piece of string. Just imagine a 400 foot long plumb line hanging from your drone. If it’s touching the ground beneath the drone, then you’re good to go. If it’s not touching the ground below the drone then you need to reduce your height. It really is as simple as that.

In their own words (taken from CAP1687)

In aviation terms, ‘height’ means the vertical distance of an object (in this case the small unmanned aircraft) from a specified point of datum (in this case above the surface of the earth). To cater for the few occasions where a small unmanned aircraft is being flown over hilly/undulating terrain or close to a cliff edge, the 400 ft height above the surface requirement may be interpreted as being a requirement to remain within a 400 ft distance from the surface, as shown in the diagram below. For the purposes of Article 94A, this is considered to be an acceptable means of compliance with the legal requirement.

Confusion has arisen from people asking the ‘top of cliff’ question; “If I take off from the top of a 300 foot (AMSL) cliff, and fly the drone to 300 foot above me (300ft AGL), can I then fly past the edge of the cliff, over the sea at 600 feet?”. The rules are clear. No! That would then mean your drone is now 600ft AGL so 200ft over your legal limit and 100ft beyond the buffer zone intended to keep drone flyers and general aviation apart!

Be sensible, fly safe, keep this wonderful hobby and industry growing and help to keep the public opinion of drones in the good stories rather than the scare stories that are too familiar.