Yes, my bad. It’s actually height.
More specifically, height above the point at which the drone is turned on.
I was also wrong on another account, I double checked and the limit is 500 metres, not 400. Not that it makes too much difference…
Out of the box, it is set to 120m so that’s close enough to 400ft. This value can be changed very easily within the app you use to control the drone, no hacking or anything is required. It’s just there in the menu.
I can’t speak for other drone brands, however DJI is by far the biggest player in the drone world so it’s most likely that you’ll encounter a DJI product.
height above the point at which the drone is turned on.
I was just about to ask: any implementation of “height above ground” would require a whole earth terrain map to be stored, which is possible but at some half reasonable resolution it is several GB (looking at e.g. the database in X-Plane) which is simply not going to be in a drone.
So they have done the simple solution. They grab the GPS altitude when it is turned on.
500m is 1600ft and the most common UK PPL cruise altitude (regardless of terrain ) is 1500-2000ft which most sensible pilots fly above anyway But yes this is obviously a problem if operated around airports, both little ones and big ones – depending how well the geofencing works.
However even 500ft is a problem in some places e.g. the place where they fly from the hill near Shoreham Airport, where SFC+500ft places you into the left base for 20. That spot has always been a problem, with all kinds of model aircraft over the years. One is relying on the flyers being at least a bit smart. Actually IIRC they are not supposed to fly above where they are, only into the valley below.
at some half reasonable resolution it is several GB (looking at e.g. the database in X-Plane) which is simply not going to be in a drone.
Why not!? It fits easily on a SD card. (Ok, SDHC.) Modern aviation GPS systems like G1000 and GTN do that…