Flying uphill and keeping to the 120m above ground rule

[MartinNWales]

I just wanted to check the right way to achieve this. I am doing a flight from a starting height of 55m (we are in the foothills of North Wales) and opposite is a smallish mountain that tops out around 100m or so.

With the flying guidance that you can fly 120M above the ground, once i crest that hill i should be able to ascend to 220m (based on 120m) above ground rather than sea level.

The app caps my height at 120m above sea level, and i'm not sure what the correct thing to do is here to allow the drone to ascend to the full height? Currently annoying sheep if i go futher at daisy cutting height so i turn around, and with the undulations around here i will often be flying low to high. Any suggestions appreciated. Link to video below so you can see the terrain..

Flight up the hill

 

[MA2 317]

Bump the max level up in the app so you can fly higher.

I have to do this when flying at a lake in the valley and fly up to the top of the hill.

Although I might be 1000 feet above my launch point once I get to the top, I'm within 400 feet of the terrain.

.

 

[Deleted member 103366]

The app caps my height at 120m above sea level,

That is incorrect, all heights displayed ANYWHERE in the app are relative to the take off point only, the drone knows nothing of the height above sea level.
As MA2 317 suggests, you simply change the maximum height to whatever meets the flight's needs.
Note, wind speeds tend to increase with height, so bear that in mind when flying high. Remember also that if 400ft above that hill top and coming home the drone must descend to remain within the 400ft above the ground layer.
I would go up to 100ft+ above ground before flying over sheep, if they are disturbed then climb higher.

 

[Meta4]

The app caps my height at 120m above sea level, and i'm not sure what the correct thing to do is here to allow the drone to ascend to the full height?

Sea level is irrelevant and the drone and app don't know what sea level is.
All heights are relative to your launch point.

 

[timsewell]

Under CAA rules your max altitude is measured from the *closest* surface. So if flying off the side of a 200m hill you could ascend to the 120m max directly above your launch point, but if you fly in the same direction as the hill's downward slope, you should adjust your height so that - looking straight down - you remain at a max of 120m.

From the CAA website:

"Your drone or model aircraft must never be more than 120m (400ft) from the closest point of the earth’s surface.

If you fly where the ground falls or rises, such as over hills, mountains or cliffs, you may need to adjust your flight path so that your drone or model aircraft is never more than 120m (400ft) from the closest point of the earth’s surface."

As other posters have noted, your app calculates height from your launch point, so as long as you stick to the above rules, you could, indeed, adjust your maximum allowable altitude to 120m above the highest point you'll be overflying and still be within the law.

 

[Deleted member 103366]

That's actually quite interesting and sensible, it allows the drone to be more than 400ft AGL when over a slope or 'near' a cliff etc..

 

[timsewell]

That's actually quite interesting and sensible, it allows the drone to be more than 400ft AGL when over a slope or 'near' a cliff etc..

No, that's exactly what it doesn't do. The drone can be more than 400ft above its launch point (which is what the app and drone calculate altitude from), but never more than 400ft above ground level, ie the bit of ground vertically below it.

 

[Deleted member 103366]

On a piece of paper draw a circle of any radius then draw a slope such that the slope is a tangent to the circle. Draw a vertical line from the centre of the circle downwards until it touches the slope. Compare the length of that line to the radius of the circle.
Which has the greater length, the radius or the line?

 

[Meta4]

No, that's exactly what it doesn't do. The drone can be more than 400ft above its launch point (which is what the app and drone calculate altitude from), but never more than 400ft above ground level, ie the bit of ground vertically below it.

Are you sure about that?
The piece you cited says nothing about a vertical measurement below the drone.
Here it is again:
Your drone or model aircraft must never be more than 120m (400ft) from the closest point of the earth’s surface

 

[timsewell]

I take 'the closest point of the earth's surface' to mean the closest horizontally to the position of the drone, ie directly below it, which would be supported by the illustration used on the CAA page.

View attachment 1641987238640.png

 

[Meta4]

I take 'the closest point of the earth's surface' to mean the closest horizontally to the position of the drone, ie directly below it, which would be supported by the illustration used on the CAA page.

Presumably you meant vertically rather than horizontally.

The closest point of the earth's surface is very particular language and used for a reason.
It would have been very easy to say the distance to the ground directly below the aircraft, if that's what they meant.
There is another illustration from CAA (that I cannot find atm), and it shows the closest, not the distance directly below.
Someone might be able to find and post it.

 

[MaximusCZ]

Draw a 120m sphere around your drone. If earth is anywhere in the sphere, you are in the green.

If you are flying near a completely vertical cliff thats 1km high, you can ascend for a 1 km as long as you are within 120m of said cliff.

 

[Phantomrain.org]

There is a Picture that @Meta4 sometimes post that shows this clearly and puts all this into perspective where is that?
I use to keep it but lost it on my last computer upgrade on the mac.

Phatnomrain.org
Gear to fly in the Rain

 

[zocalo]

I've always used 120m in the vertical direction (or whatever the local equivalent is) as that meets both "nearest" and "AGL" criteria, which is how I've always interpreted the image posted above. As other posters have noted though, that can be problematic if you go over the top of a sheer cliff as your AGL altitude will rise dramatically, and, in the worst case scenario, if 120m AGL is the letter of the law, then if the cliff is more than 120m high then you should not fly over the edge regardless of your AGL at the clifftop.

That might be kind of silly from a proxmity to other aircraft point of view, but is *very* sensible if there might be people or animals at the foot of the cliff. Especially so when you take into account that cliffs can often produce updrafts which, in turn, are going to increase the chances of you losing control of the aircraft.

Even so, I'd be quite interested if there is any more specific guidance in the scenario of radical terrain induced AGL changes as it's one I come across fairly often and having a little more leeway could be useful (noting that, as the pilot, I would still be responsible for the flight being safe, naturally!)

 

[MAvic_South_Oz]

There is a Picture that @Meta4 sometimes post that shows this clearly and puts all this into perspective where is that?
I use to keep it but lost it on my last computer upgrade on the mac.

Phatnomrain.org
Gear to fly in the Rain

Like this ?



Not sure if this is current or old.

 

[Phantomrain.org]

Like this ?

View attachment 141818

Not sure if this is current or old.

Like this but with the guy at the bottom of the hill , but this should help also.

Phantomrain.org
Gear to fly in the Rain.

 

[bmwbob]

I flew my air 2 up some hills well over 400 feet, but well under 400 feet AGL and went through hell getting it to descend and nearly lost it!

 

[sar104]

Like this ?

View attachment 141818

Not sure if this is current or old.

That is the current UK interpretation:

Flying where there are hills, mountains or cliffs​

Your drone or model aircraft must never be more than 120m (400ft) from the closest point of the earth’s surface.

Where you can fly drones | UK Civil Aviation Authority

Find out about height limits and distances from people, buildings, crowds and vehicles. Restrictions on flying drones and model aircraft near airports.

register-drones.caa.co.uk

 

[snowghost]

If you're more than 400' away from a 200' high hill , (in VLOS of course), can you still climb to 600' (400' above the hill)?

 

[MaximusCZ]

If you're more than 400' away from a 200' high hill , (in VLOS of course), can you still climb to 600' (400' above the hill)?

It doesnt matter where you are. Your drone must be 120m (or 400 feet) to nearest surface.