DJI Mavic, Air and Mini Drones
Friendly, Helpful & Knowledgeable Community
Join Us Now

UK - AGL rules for *manned* aircraft near hilltops?

zocalo

Well-Known Member
Joined
Sep 30, 2018
Messages
917
Reactions
1,070
To set the scene, ~2 months ago I moved to live in a rural area near the summit of a line of hills and, since the views are rather good, frequently fly my drone either from the property itself or, if unoccupied by livestock, from one of the adjacent fields which are part of our neighbour's farm. Our property is at about 320m above sealevel, around 200m above the valley floor, and the hill I'm on peaks at around 360-380m, depending on where you cross the ridge.

Besides a few instances when I wasn't flying my drone, I've had to deconflict twice now due to aircraft (both times a helicopter, not that it really matters) approaching at below 500ft AGL, and in the most recent instance, visibly below the height of my drone which is capped at 120m from takeoff point, and was close to max altitude over its take-off point at the time, e.g. ~400ft AGL, as I was getting some top-down views of the property and grounds. I would assume the pilots doing this are at a reasonable AGL for the valley floor on either side of the ridge, but simply maintain that as they fly over the ridge as I seldom notice any visible change in altitude as they approach.

To be clear, I get that the responsibility is on me to deconflict in this situation, and my SOP is to reduce altitude as appropriate whenever I hear an approaching aircraft no matter where I am anyway, but my understanding is that aircraft pilots also have a responsibility to do things like avoiding structures, such as our property or the farm slightly further down the hill, and potentially disturbing livestock, like the farm's dairy herd - some of which were definitely slightly spooked during the latest flypast.

I know drone limitations are strictly AGL and closest point of approach based (and the CAA's diagrams make this perfectly clear), but is it OK for manned light aircraft pilots to maintain level flight over hilltops, even though that might briefly bring them within 500ft of ground level and/or structures, or should they be increasing altitude to maintain 500ft AGL regardless?

Also, while I would hate to tempt fate and/or give the anti-drone crowd another datapoint in the drone-involved near miss reports that they seldom look into the details of, some guidance as to where the line is that I should raise these to the CAA as an Airprox would be appreciated. I've had two occasions where I've deconflicted as a precaution in less than two months (I wouldn't class them as a near miss as I was able to get my drone well out of the way in plenty of time), and I suspect they won't be the last.
 
@zocalo while i can sympathise with you ,regardless of whether the aircraft involved were or were not flying below the 400ft max of your drone ,unfortunately they still have airspace precedence over the drone ,emergency aircraft can fly legally under the 500ft ceiling and often do ,its the same with military aircraft as well ,its something that we as drone pilots have to accept, and now you are aware that this could happen on a frequent basis ,its up yo you to modify your AGL height so as to avoid similar instances in the future,i am not saying for one moment that you were doing anything wrong ,and you did the right thing by reducing you height or even landing to avoid a collision, in the pecking order of machines that can take to the air ,drones are pretty well at the bottom at this time
 
@zocalo while i can sympathise with you ,regardless of whether the aircraft involved were or were not flying below the 400ft max of your drone ,unfortunately they still have airspace precedence over the drone ,emergency aircraft can fly legally under the 500ft ceiling and often do ,its the same with military aircraft as well ,its something that we as drone pilots have to accept, and now you are aware that this could happen on a frequent basis ,its up yo you to modify your AGL height so as to avoid similar instances in the future,i am not saying for one moment that you were doing anything wrong ,and you did the right thing by reducing you height or even landing to avoid a collision, in the pecking order of machines that can take to the air ,drones are pretty well at the bottom at this time

Yeah, I know the pecking order here, hence my SOP of reducing altitude if I think it even slightly necessary to do so, and also the legal limits of what I can (and do) fly under. As you note, I'm pretty sure I did everything by the book and quite likely the pilots never even had a chance to realise my drone was there as a result. My main concern is an aircraft will come from the other side of the hill and the first I know about it is when it's almost on top of me, reducing my ability to deconflict considerably. As you say, I can modify my flight profile to de-risk things further, but I'm also interested in knowing exactly where things might stand in the event of something more serious to better assess just how much de-risking I might want to apply.

These were definitely civilian aircraft not military, and were not one of the local police helicopters or air ambulances either as all of those have quite distinctive colour schemes and operate from an airfield near where I used to live, so I'm quite familiar with them. My limited understanding of civilian legal flight limits is that they are *normally* supposed to maintain a minimum of 500ft AGL except when taking off or landing, and I guess when required for something like crop dusting (not that we have much of that in the UK) that needs low-level flight. Neither apply here; the hill is moorland/upper pasture and I checked for local airfields/helipads soon after moving in to get a feel for likely flight patterns; the nearest is the local hospital's helipad, about 5km away, and 4km further along the valley.

My take is that these these are civilian pilots flying between A and B and simply saving some fuel by avoiding an altitude change as they pass over a hill. That's the part of the light aircraft regulations I'm not clear on, so I guess my question is whether there are any restrictions on doing that and, if so, what they are. To my mind, that not only has an obvious bearing on my pre-flight risk assessments, but also on where I should be drawing the line before I start seriously thinking about raising an airprox.
 
  • Like
Reactions: old man mavic
@zocalo there is nothing stopping you from trying to find out what the rules are for civilian light aircraft and helis ,here in the UK ,if you feel that they are not flying in the framework of the rules governing there safe operation
 
@zocalo there is nothing stopping you from trying to find out what the rules are for civilian light aircraft and helis ,here in the UK ,if you feel that they are not flying in the framework of the rules governing there safe operation
That's basically what I'm trying to do knowing the law on both sides is going to really help with risk assessment and whether I ought to be logging an Airprox, especially if they shouldn't be getting within 500ft of the property or ground, both of which seem to be the case. I know there are a few light aircraft pilots here and I'm hoping someone can clarify what the regulations are, because I'm getting lost in the weeds trying to find something similar to the simple guidance summary that the CAA produced for drones only applicable to light aircraft, or even a summary "rulebook", via Google.

So far, the best I've got is this from a UK Parliament summary of the rules: "Generally, an aircraft may fly at a height of less than 150 metres (500 feet) above the ground or water; or less than 150 metres above the highest obstacle within a radius of 150 metres from the aircraft. However, it must not be flown closer than 150 metres to any person, vessel, vehicle or structure except with the permission of the CAA."

That seems to imply that it's OK to fly low over the hilltop, but not to approach within 150m of a property. I suspect that makes the two flights legal, as long as they didn't come within 150m of the property, which is hard to call on for the first and much less likely for the second that was low enough to spook the cattle. I can make decisions based on that if need be, but any further clarification from someone who knows the rules would certainly be helpful, especially given the potential impact on a pilot that is the subject of an Airprox.
 
  • Like
Reactions: old man mavic
To be honest, I think most pilots with light aircraft licenses would be a lot more comfortable flying well over anything on the ground, including undulating terrain etc.
150m would feel like you were about to land on it.

Most would likely plan their trip with the highest point in mind, then aim to fly 500m over that I would think.
If something goes wrong, that height gives them time to react and put a plan into action, and with most pilots concerned here having just one engine, well . . .

Helis are a different matter, but probably away from touristy spots, most of those would probably like some decent separation from the ground too while in flight.

It's the exceptions to these general pilots we need to be mindful of, they can turn up in very rare cases, but that's what could happen.
 
Last edited:
@zocalo as you are aware the rules for use of the airspace, are there to keep that environment as safe as possible ,and you are i am sure, also aware that the first 400ft AGL is where we as drone flyers are allowed to operate ,that does not mean that it is exclusive airspace ,and when an aircraft fly's over your area it can be very difficult to accurately judge its height from the ground,and irrespective of the exact height that the other aircraft was at as it flew across your property ,it is still you who has to take action to avoid a collision
 
  • Like
Reactions: Dronecation
In the US at least the 500 ft AGL rule for manned aircraft is only for densely populated areas and they really mean urban areas of cities. These areas are shown on the aviation charts. Also helicopters aren’t subject to these same rules.

I’m sure there are some differences for the rules in the UK but I bet it’s not all that much different and in a rural area I doubt there are any minimum height rules especially for helicopters.
 
You may find it here:
as to how much has changed is up to you to find amendments.
Pilots also have to consider their distance from clouds above and in front.
Whether they are on a VFR or IFR flight flight plan makes for a different flight scenario as well.
It is still your responsibility as a drone operator to take evasive action. The 100ft separation from 400ft to 500 ft is a safety buffer, but not a guarantee...
 

DJI Drone Deals

New Threads

Forum statistics

Threads
130,070
Messages
1,548,989
Members
159,127
Latest member
timvsouth