The practicalities of the 400' AGL limit in the mountains


I am a complete newbie and trying to find out more about the 400’ altitude limit. I totally understand the rules and know that we can only fly at a max of 400’ AGL. On my first flight I took the M2P up to this height to test the software and it does not go higher. However, I am a keen mountain walker and can see plenty of opportunities for using my M2P when out walking. But, say for example I am walking along a ridge at 2000’ AGL and there is a very steep 500’ drop off to one side. I know that I can fly the drone at a max of 400’ above me but if I decide to film from the side i.e. by taking the drone over the drop, will it suddenly sink as it would now be over 400’ AGL? I don’t want to be caught out. Similarly, I have walked many knife edge ridges with very steep drops either side. How does the sensor cope with this? If anyone has flown their drone in such an environment with the software restricted to 400’ AGL it would be nice to here from you. Thanks for reading.


The drone will fly, treating the level you took off from as AGL.
But according to the “Drone Code”, you must not fly above the 400 ft if the ground is contoured.
(That is assuming you are not above it’s max ceiling height.)
If you fly sideways then say down 100 ft, the App should show that you are fly at -100ft.
I have flown from off Cliffs then down and my height has shown as a minus figure in altitude.


I have flown in many countries (Norway, Finland, Switzerland) ,at 2,000 + metres altitude.
But never encountered a problem.
If you look in the Member Only section, you will find many useful Documents that I have put together to make your Flying Experience better.
And by the way !, Welcome to GADC !, pull up a chair, pour some wine and browse.
You will find many posts that may be of relevance to your problems.

This post may answer your questions on AGL as far as the “Drone Code” states.


Thanks Chris for your quick response. To know that the drone will not suddenly reduce altitude to 400’ AGL if you fly it over a high cliff is very helpful. I want to avoid contravening the code and my next question was to be, if I flew over the cliff and reduced altitude to comply with 400’ AGL, would I have to land and walk down and get. Not always practicable. To know that the altitude limit can be overridden in the Go 4 app is very useful and would help me avoid walking down the mountain to recover the drone. But I need to avoid getting into this situation in the first place!


Hope this helps


Hello and welcome, as Chris has said it will not drop, you will just be breaking the drone code, stupid rules should be replaced with common sense I think myself, how else do we get the killer shot we want when walking on a ridge if we follow the latest stupid rule.


The drone code recommendations are somewhat stupid in the situation you are talking about !.
And more often than not, not practicable to be carried out , especially if you are in a the Mountains, with not a soul in sight for miles!.
I think common sense has to prevail in those situations and each one has to be done on it’s merits at the time.
As @MementoMori said, if you want “That Shot”, I would say go for it !, I have on many occasions.


I would agree.


Life was far less complicated when this rule applied:

To be clear, the image I posted here was within the old drone code rules but it now falls foul of the new drone code rules.


I had a situation in Tromso, Norway a couple of years back. Halfway up a Mountain, rang Tromso Airport ATC, got clearance to fly. Asked what height am I clear for “What height would you like to fly to, Sir!”
(Max at the time 500 meters) “Would 1,500ft be ok for the next 15 mins”…“Yes, Sir, you are cleared for 1,500 feet for the next 15 mins, we have no incoming traffic in our area for 25 miles”.
Got my killer shot at 1,500 ft !, down with the drone, in the bag and away.
Rang Tromso ATC and thanked them for there time.
Moral: You never get, if you don’t ask !.
Would not get away with it now though, with the change of rules, etc

I should have added, that my Brother-in-Law was acting as spotter for me at the time.




I should clarify that Ididn’t just unpack the M2P and fly away at 400’. I went through three batteries practicing in an open field and the last thing before packing up was to go vertically to 400’ from the take off poitn and back straight back down again to the same position. I have to say that I was somewhat anxious though!

@PingSpike - thanks for the sketch, reminds me of North Wales! I have to say that the old rules make more sense but I suppose there is little chance of getting them changed. I am a member of some of the Hillwalking forums and it is amazing how many members a dead against drones in the mountains.


The beauty of a walk in the mountains is the peace and tranquillity it provides, an escape from the normal lifestyle so I understand why they don’t like it.
however the countryside / mountains are large enough for everyone to enjoy responsibly.


Indeed they did.

I’m pretty sure a 1KG drone falling on your bonce from 900ft is going to hurt no more than a drone falling on your from 400ft :roll_eyes:


My only concern here is that in the lakes and occasionally in the Dales I have looked down on training aircraft and seen the pilots waving :astonished:


I don’t want to be a buzzkill, but as someone who regularly flys full size all I can say is: if Drones stick to the 400ft rule and full size sticks to the 500ft rule, then all is well
It’s a big sky I know, but I do sometimes worry when I’m bimbling around at low level in the Brecon Beacons and I can tell you it’s a different level of worry when you are actually up in the sky looking down rather than stood on solid ground with only how much money you will lose to worry about

Hope that doesn’t sound judgemental, but some of the videos on youtube send a chill down my spine.

One thing I have been involved with is electronic conspicuity devices in man carrying aircraft, I use a device called pilotAware and also a mode S transponder with ADSB Out, the tech is becoming lightweight and low power and I am sure will be adopted by Drones at some point, it has to become widely adopted to be of real use but would go a long way towards making the combined use of airspace safer for all concerned

Sorry going a bit off topic, but a subject close to my heart.


I don’t believe I ever said I go above 400ft, you may have misunderstood.
What I meant was if you take off from one of the beacons and fly to 50ft and then out 300ft for instance I bet you would be above 400ft agl, this is the only time I would see me possibly being above 400ft even though I didn’t intend to.


The law is, in this case, as they say, an ass.

The diagram that @MertOzkan published is the key and it shows the devil in the detail that you describe. That diagram is supposed to suggest that as you fly off the top of that hill and the ground slows gently away from you, you are supposed to reduce your altitude in a nice gentle way that runs parallel to the ground and maintains your 400ft AGL position. Sounds great to some officious bureaucratic muppet behind a desk in Whitehall, but the real world isn’t like that.

Fly off a cliff edge, and suddenly it becomes obvious how stupid that rule is. Suddenly you’re way above max permitted altitude and feeling a bit like Wylie E. Coyote in a Roadrunner cartoon when he goes off the edge of a cliff and hangs in midair for a second. You’re expected to drop like a stone. It’s bloody silly.


Sorry Memento I didn’t mean to imply you would behave that way, but rather illustrate one reason why such rules exist.
I agree that its far from a perfect situation, but it’s early days
Realisticly rules are worthless in the current situation as the widespread availability of Drones is almost guaranteed to result in many being in the hands of irresponsible idiots and there is no practicle means of stopping this, the genie is out of the bottle

I don’t include the good people of this forum in the above description and wish you many happy hours of flying


I do apologise for the length of this post but I do believe that having a full understanding of the rules when flying off mountains and hills is important.

It appears to me that there are two interpretations of the 400’ AGL rule when flying a drone in hilly or mountainous areas. Basically, it boils down to how AGL should be measured. In the diagram posted by #MertOzkan and which was produced by the CAA, it clearly indicates (to me anyway) that the 400’ is measured between drone and ground parallelly. Thus, the 400’ AGL line follows the terrain below it in the form of a contour line. When contour flying at 400’ AGL, vertical height, but not parallel AGL height, may exceed 400’AGL occasionally on steep ground. I believe this is acceptable and does not contravene the DroneSafe code. However, I am a newbie to drone flying so happy to be challenged but I have had 35 years’ experience in interpreting and applying the law.

The other interpretation suggests that the 400’ AGL height is measured with an imaginary plumb line dangling from your drone. Adhering to this interpretation on steep ground, would bring your drone very close to the hill, cliff or whatever and potentially pose a risk to climbers, walkers etc. who may not be in your line of sight although you still have sight of your drone. This interpretation does not make sense to me.

The ‘plumb line’ interpretation is supported by But I think they’ve got it wrong (says a mere newbie). They support their case by saying that if you don’t abide by their ‘plumb line’ you could enter the buffer zone between drone and manned AC. They have produced an interesting little diagram which you can find using the above link.

I have amended their diagram to support my argument that if both drone and AC abide by the rules i.e. 400’AGL for drones and minimum of 500’ AGL for manned AC there will not be a problem. Note that military AC may well be below 500’ AGL when flying in the mountains. You need to know the routes they use, but they are generally well publicised .

In my diagram, I have added a another contour line above the 400’ AGL line and this represents the 500’AGL being the minimum height for civil AC (certain exceptions excluded) and hopefully shows that if the 400’ and 500’AGL heights are measured parallelly and airspace users stick to it, there should not be any conflict even though at times drones may well be over 400’ AGL when measured vertically.

Finally, I have decided that to give me plenty of height in reserve when flying off a ridge or peak, generally there is little point going up to 400’ AGL as after all you are pretty high up anyway.

Look forward to your views and any other interpretations!