What do we mean by "altitude" ?

[JIS_en_France]

So the maximum altitude I am permitted to fly is 120 metres ie 400ft. However, was does this mean ? If I take off from my back garden and fly north, there are hills which rise up and, despite starting my flight at 30m / 100ft , I have to gain altitude to avoid trees. Indeed to maintain signal strength and to be sufficient high above roads and houses, I can often reach 160m / 525ft. However this is not more than 30m above the actual land; but it is 160m higher than my original take-off point. So, what do the oathirities mean my altitude ? Above the land below or above sea level ? If it were the latter many of us would never be able to fly in hilly / alpine areas ?
Thanks for your thoughts
John

 

[Interficiam Stercore]

Altitude above AGL or Above ground level. See Picture.View attachment 132711

 

[JIS_en_France]

Thanks; that makes sense. Hovere with the Mini2 only showing altitude from the take off point it's clearly a matter of judgement ! No ?

 

[Interficiam Stercore]

Thanks; that makes sense. Hovere with the Mini2 only showing altitude from the take off point it's clearly a matter of judgement ! No ?

Yes, because drones only judge their height from their initial barometer readin where you took off, You will have to guess how high you are from the side of a mountain to the elevation of your drone. But don't worry, If your 100ft too high, there is no way anyone would be able to know if you're exceeding the altitude limit. Even if they thought you were, they couldn't prove it.
EDIT- Well, as BigAl said, they could use your flight records and elevation maps if there was an accident severe enough to get the NTSB involved and an inquiry following that mishap. So, they could prove what your exact altitude was.

 

[BigAl07]

Altitude above AGL or Above ground level. See Picture.View attachment 132711

that's the WRONG graphic!! That is for other areas/countries and does NOT accurately depict FAA regulations. Notice the one aspect where the arrow is pointing from the side of the hill showing 400'. That is not AGL which clearly means Above Ground Level.

AGL is to the piece of ground/terra firma directly UNDER the aircraft itself. Not from the bank, hill, mountain laterally etc but UNDER THE AIRCRAFT!

The best way to "visualize" this is to imagine a fixed piece or rope, string, cable etc that is exactly 400' long hanging from the bottom of your aircraft. If at any time during your flight that rope, string, cable etc is not touching the ground you are no longer flying within FAA regulations of 400' AGL (unless other circumstances are in play, Commercial rules etc).

 

[BigAl07]

Thanks; that makes sense. Hovere with the Mini2 only showing altitude from the take off point it's clearly a matter of judgement ! No ?

It's completely a judgement call and easier to just operate on the side of caution.

Keep in mind that if there is an incident involving you and your UAS, your logs can be pulled and compared to terrain maps to determine a more accurate (tongue in cheek) altitude you was flying at. That's why it's better to error on the side of caution.

 

[Interficiam Stercore]

that's the WRONG graphic!! That is for other areas/countries and does NOT accurately depict FAA regulations. Notice the one aspect where the arrow is pointing from the side of the hill showing 400'. That is not AGL which clearly means Above Ground Level.

AGL is to the piece of ground/terra firma directly UNDER the aircraft itself. Not from the bank, hill, mountain laterally etc but UNDER THE AIRCRAFT! I.S. Edited Graphic

See EDITED Graphic. I believe this is now Correct. I used Photoshop to change the arrow direction.

 

[Zbip57]

Yup, it's 400' Above Ground Level. That's a vertical measure, as if you have a 400' string hanging from the bottom of your drone. The USA's FAA, I believe, allows an extra 400' above buildings or structures (like for tall radio tower inspections), as long as you stay within a 400' radius of that structure, the reasoning being that other manned aircraft shouldn't be that close to structures anyway.

In Canada, of course, we like to be similar but different than the USA. Transport Canada imposes the same 400' AGL ceiling, unless you have extra permission via a Special Flight Operations Certificate. However, we permit only an extra 100' (30m) above any building or structure within a 200 feet (61 m) distance of the building. Why not simply copy the same numbers from the FAA? grrrrr.
See this regulation: laws-lois.justice.gc.ca/eng/regulations/SOR-96-433/page-180.html#h-1111736

Even though both countries clearly specify AGL in each case, I think neither one makes any sense with respect to lateral distance from surface features versus building structures.

AGL is to the piece of ground/terra firma directly UNDER the aircraft itself. Not from the bank, hill, mountain laterally etc but UNDER THE AIRCRAFT!

The best way to "visualize" this is to imagine a fixed piece or rope, string, cable etc that is exactly 400' long hanging from the bottom of your aircraft. If at any time during your flight that rope, string, cable etc is not touching the ground you are no longer flying within FAA regulations of 400' AGL (unless other circumstances are in play, Commercial rules etc).

Both countries explicitly refer to 400' ABOVE ground, which is measured vertically. It doesn't say 400' away sideways from the ground. So, if you're flying up a sloped hillside you'd need to stay within 400' vertically above the surface, like this:

But, what's ridiculous is that this vertical interpretation also implies that you must stay much closer to a more steeply sloped hill like this:

If it's a vertical cliff you can legally fly up to 400' from the valley floor, and you can fly 400' above the clifftop plateau, but you cannot legally fly from one to the other if the cliff face is taller than 400'.
But here's what's stupid about such a strict interpretation. Instead of a vertical ground feature (i.e. cliff), if the exact same obstruction is a building structure, then the FAA says you are allowed to fly within 400' laterally of the side of the structure, like this:

So why is one allowed, but not the other?

 

[Zbip57]

So why is one allowed, but not the other?

Here's another confusing example.

If it's a pyramid-shaped ground feature, the FAA says you can fly 400' AGL vertically above the ground surface up and over the pyramid. The steeper the hillside, the closer you need to stay laterally,


But if it's a pyramid-shaped building structure, you can also fly as much as 400' laterally away from the sides of the structure.

So, assuming you had permission to fly over the glass pyramid in Memphis Tennessee, you could fly as much as 400' above and 400' laterally of this pyramid because it's a building structure.


But here's a tricky one. The largest pyramid in the world (by volume) is in Mexico. But it was only quite recently discovered (1910) as it was entirely covered in dirt.

So, if it looks like an earthen hillside taller than 400' the FAA says you are allowed to overfly the thing as long as you stay within 400' vertically of the surface. But if it turns out to actually be a "structure", only then are you allowed to also fly as much as 400' laterally from the surface.

What the...?

Why not simply say you must always stay within 400' AGL and within 400' laterally of any obstructions taller than 400'?

 

[BigAl07]

Yup, it's 400' Above Ground Level. That's a vertical measure, as if you have a 400' string hanging from the bottom of your drone. The USA's FAA, I believe, allows an extra 400' above buildings or structures (like for tall radio tower inspections), as long as you stay within a 400' radius of that structure, the reasoning being that other manned aircraft shouldn't be that close to structures anyway.

Ummm easy there sparky... let's get more facts involved and not go half way in on this topic. . . .

That "allowance" is only for Part 107 Operations and it is used to allow "Tower/Utility Inspections" by Commercial Operations ONLY! We don't inspect many hills, mountains, trees, etc so there is no need for such an allowance and the wording is very specific and intentional to state "Structures" and "Structures" are defined by the FAA as to not have any grey area.

Also it's important to note that within the USA (FAA rules) flying an additional 400' (for a Commercial Operator) over a structure does NOT allow the operator to go any higher than the approved height if in Controlled Airspace. For example:

I'm flying at KAVL in a 100' LAANC Grid Area. I apply for and get approval to fly up to 100' AGL for a Part 107 flight in that area. It just happens there is a 75' Cellular Data Tower in that same grid which I am hired to collect data about. Even though in most areas (Uncontrolled airspace) I can go up to 400' OVER the height of the structure (100'), the Altitudes in an Authorization are ABSOLUTE! You can NOT go over the approved height what so ever! The MOST I could go over the tower would be an additional 25'AGL( 75' of tower plus 25' gets me up to the 100' Authorization height) if I am to remain safe and legal.

 

[Interficiam Stercore]

That "allowance" is only for Part 107 Operations and it is used to allow "Tower/Utility Inspections" by Commercial Operations ONLY! We don't inspect many hills, mountains, trees, etc so there is no need for such an allowance and the wording is very specific and intentional to state "Structures" and "Structures" are defined by the FAA as to not have any grey area.

Also it's important to note that within the USA (FAA rules) flying an additional 400' (for a Commercial Operator) over a structure does NOT allow the operator to go any higher than the approved height if in Controlled Airspace. For example:

I'm flying at KAVL in a 100' LAANC Grid Area. I apply for and get approval to fly up to 100' AGL for a Part 107 flight in that area. It just happens there is a 75' Cellular Data Tower in that same grid which I am hired to collect data about. Even though in most areas (Uncontrolled airspace) I can go up to 400' OVER the height of the structure (100'), the Altitudes in an Authorization are ABSOLUTE! You can NOT go over the approved height what so ever! The MOST I could go over the tower would be an additional 25'AGL( 75' of tower plus 25' gets me up to the 100' Authorization height) if I am to remain safe and legal.

Lets us not forget the recreational pilot. They are locked at 400 ft AGL period. When it comes to man made structures they cannot go over, just around. They don't get to use the Parrt 107 rule of 400ft above and laterally. I sorta remember being told this factoid. Is it right? Or, maybe it's allready been mentioned in the thread. I just couldn't read it all.

 

[BigAl07]

Lets us not forget the recreational pilot. They are locked at 400 ft AGL period. When it comes to man made structures they cannot go over, just around. They don't get to use the Parrt 107 rule of 400ft above and laterally. I sorta remember being told this factoid. Is it right? Or, maybe it's allready been mentioned in the thread. I just couldn't read it all.

Uhhhh it's pretty much the same thing you quoted of mine but said in a different way

 

[Zbip57]

Ummm easy there sparky...

Sparky?

That "allowance" is only for Part 107 Operations and it is used to allow "Tower/Utility Inspections" by Commercial Operations ONLY!

I realize this allowance was originally requested by, and created for, people doing tower inspections. But the wording in § 107.51 says;

(b) The altitude of the small unmanned aircraft cannot be higher than 400 feet above ground level, unless the small unmanned aircraft:
(1) Is flown within a 400-foot radius of a structure; and
(2) Does not fly higher than 400 feet above the structure's immediate uppermost limit.

Where are you seeing that this allowance can ONLY be used for "Tower/Utility inspections"?

We don't inspect many hills, mountains, trees, etc so there is no need for such an allowance

Maybe you don't have any hills, mountains, or trees taller than 400' in North Carolina. But, just for hypothetical argument's sake, let's assume you are surrounded by a forest of 400' tall trees. By your interpretation a recreational flyer would not be permitted to fly a drone above this forest as that would be exceeding the 400' AGL ceiling. Are you also saying that manned aircraft, which should normally fly higher than 500' AGL, would then be allowed to skim a mere 100' over the treetops of this forest?

... the wording is very specific and intentional to state "Structures" and "Structures" are defined by the FAA as to not have any grey area.

Can you provide a link to this FAA definition of "Structures"?

 

[Zbip57]

Lets us not forget the recreational pilot. They are locked at 400 ft AGL period. When it comes to man made structures they cannot go over, just around. They don't get to use the Part 107 rule of 400ft above and laterally.

So here's my pyramid-shaped hill again. Assuming you're not intruding into any upper level controlled airspace, the FAA says even a recreational pilot can fly up vertically to 400' AGL above any hill like this.



But if it's a man-made "structure" of the exact same shape, a recreational pilot would be forced to fly AROUND it???


You don't find that absurd?

 

[BigAl07]

Sparky?


I realize this allowance was originally requested by, and created for, people doing tower inspections. But the wording in § 107.51 says;

(b) The altitude of the small unmanned aircraft cannot be higher than 400 feet above ground level, unless the small unmanned aircraft:
(1) Is flown within a 400-foot radius of a structure; and
(2) Does not fly higher than 400 feet above the structure's immediate uppermost limit.

Where are you seeing that this allowance can ONLY be used for "Tower/Utility inspections"?

Maybe you don't have any hills, mountains, or trees taller than 400' in North Carolina. But, just for hypothetical argument's sake, let's assume you are surrounded by a forest of 400' tall trees. By your interpretation a recreational flyer would not be permitted to fly a drone above this forest as that would be exceeding the 400' AGL ceiling. Are you also saying that manned aircraft, which should normally fly higher than 500' AGL, would then be allowed to skim a mere 100' over the treetops of this forest?


Can you provide a link to this FAA definition of "Structures"?

Seriously? LOL!

ONLY was for "Only Part 107" so let's not attempt to further muddy the waters. I didn't say it's ONLY used for "Tower/Utility inspections". We're better than that . . . .

A MANNED aircraft, if flying at mins altitude, is expected to maintain that height above anything on the ground.... so to fly at say 500' they would maintain that over anything protruding from the ground (house, trees, tower, etc). Of course it would be an estimation but the manned aircraft pilot would attempt to remain that height above ground obstacles.

You'll have to use GOOGLE to find that definition but IIRC it's mentioned a couple of times in reference to Airport Obstructions etc.

 

[BigAl07]

So here's my pyramid-shaped hill again. Assuming you're not intruding into any upper level controlled airspace, the FAA says even a recreational pilot can fly up vertically to 400' AGL above any hill like this.
View attachment 132784


But if it's a man-made "structure" of the exact same shape, a recreational pilot would be forced to fly AROUND it???
View attachment 132785

You don't find that absurd?

Yes exactly right!

 

[Zbip57]

Seriously? LOL!

ONLY was for "Only Part 107" so let's not attempt to further muddy the waters. I didn't say it's ONLY used for "Tower/Utility inspections". We're better than that . . . .

Ah, okay that makes more sense, sort of...

A MANNED aircraft, if flying at mins altitude, is expected to maintain that height above anything on the ground.... so to fly at say 500' they would maintain that over anything protruding from the ground (house, trees, tower, etc). Of course it would be an estimation but the manned aircraft pilot would attempt to remain that height above ground obstacles.

But that just proves my point, doesn't it?

The whole idea behind the 400' AGL ceiling for unmanned aircraft is to maintain a safe 100' separation from manned aircraft which should (generally) be flying more than 500' AGL. And that 500' height for manned aircraft is measured above any ground obstacles.

If there is a 500' tall apartment building in the way, manned aircraft cannot just buzz across inches above the roof at 500' AGL. They have to climb an additional 500' to 1000' AGL to safely clear that ground obstacle.

So in my hypothetical example of a forest with 400' tall trees, manned aircraft should stay at least an additional 500' higher than the treetops (i.e. 900' above the ground surface). Why then should unmanned recreational aircraft instead always be restricted to 400' AGL measured from the earth's surface, rather than also from the top of any ground obstacle?

If it's a 400' tall hill, unmanned aircraft are allowed to fly up to an additional 400' above any hilltop, as that is still the same 400' AGL measured above the earth's surface (above the hilltop).

But if it's a similarly shaped 400' tall man-made pyramid, everyone insists the regulations are clear and recreational drones must fly around that particular man-made ground obstacle, because recreational flyers are never permitted to fly above 400' AGL, even though the 500' airspace above any ground obstacle is supposedly otherwise safely clear of manned aircraft.

That's the bit that I find absurd.

I know I've mentioned this many times, but in Canada we no longer have any distinction between Recreational vs Commercial drone operations. The exact same regulations apply equally regardless of intent. The only major difference is between the easier Basic operations versus Advanced operations. With only a Basic certificate you cannot fly within any controlled airspace. If you need to fly there, then you must hold an Advanced certificate.

Even the Canadian allowance for flying higher over structures taller than 400' applies equally to both Basic or Advanced operations (again regardless of recreational vs commercial intent), unless that additional height puts you into an overhead controlled airspace. Controlled airspace always requires an Advanced certificate as well as coordination with the airspace controller.

But, if you're flying drones under 250 grams, none of those Basic or Advanced regulations apply at all. Only the "Don't be Stupid" rule still applies. Don't interfere with manned flight and don't be a hazard to people on the ground. There is no actual legal restriction specifically limiting AGL height when flying sub-250g, other than the obvious "Don't be Stupid" rule.

That's why I find it so odd that you still have this bizarre distinction between recreational and commercial drone operations with weird interpretations of recreational flyers not being allowed to fly above a forest if the trees are taller than 400' because that would exceed their 400' AGL restriction. Oh no, you'd need a Part 107 commercial permit for that...

Can you provide a link to this FAA definition of "Structures"?

You'll have to use GOOGLE to find that definition but IIRC it's mentioned a couple of times in reference to Airport Obstructions etc.

I tried that, but I can only find references to "structures" within CFR Part 77. I was just curious if there's actually an official legal definition. In the USA, recreational flyers can fly over a 400' tall hilltop, but not over a 400' "structure". Hmmmm ?

 

[Zbip57]

Actually, all of this is totally irrelevant to the original poster's question. The rules in Canada vs USA won't make any difference to him as he's in France. ?

 

[dronerdave]

Actually, all of this is totally irrelevant to the original poster's question. The rules in Canada vs USA won't make any difference to him as he's in France. ?

Drone Laws in France | UAV Coach (2023)

Want to learn more about drone laws in France? Check out our list of links and regulations for people flying drones in France.

uavcoach.com

 

[BigAl07]

Ah, okay that makes more sense, sort of...


But that just proves my point, doesn't it?

The whole idea behind the 400' AGL ceiling for unmanned aircraft is to maintain a safe 100' separation from manned aircraft which should (generally) be flying more than 500' AGL. And that 500' height for manned aircraft is measured above any ground obstacles.

If there is a 500' tall apartment building in the way, manned aircraft cannot just buzz across inches above the roof at 500' AGL. They have to climb an additional 500' to 1000' AGL to safely clear that ground obstacle.

So in my hypothetical example of a forest with 400' tall trees, manned aircraft should stay at least an additional 500' higher than the treetops (i.e. 900' above the ground surface). Why then should unmanned recreational aircraft instead always be restricted to 400' AGL measured from the earth's surface, rather than also from the top of any ground obstacle?

If it's a 400' tall hill, unmanned aircraft are allowed to fly up to an additional 400' above any hilltop, as that is still the same 400' AGL measured above the earth's surface (above the hilltop).

But if it's a similarly shaped 400' tall man-made pyramid, everyone insists the regulations are clear and recreational drones must fly around that particular man-made ground obstacle, because recreational flyers are never permitted to fly above 400' AGL, even though the 500' airspace above any ground obstacle is supposedly otherwise safely clear of manned aircraft.

That's the bit that I find absurd.

I know I've mentioned this many times, but in Canada we no longer have any distinction between Recreational vs Commercial drone operations. The exact same regulations apply equally regardless of intent. The only major difference is between the easier Basic operations versus Advanced operations. With only a Basic certificate you cannot fly within any controlled airspace. If you need to fly there, then you must hold an Advanced certificate.

Even the Canadian allowance for flying higher over structures taller than 400' applies equally to both Basic or Advanced operations (again regardless of recreational vs commercial intent), unless that additional height puts you into an overhead controlled airspace. Controlled airspace always requires an Advanced certificate as well as coordination with the airspace controller.

But, if you're flying drones under 250 grams, none of those Basic or Advanced regulations apply at all. Only the "Don't be Stupid" rule still applies. Don't interfere with manned flight and don't be a hazard to people on the ground. There is no actual legal restriction specifically limiting AGL height when flying sub-250g, other than the obvious "Don't be Stupid" rule.

That's why I find it so odd that you still have this bizarre distinction between recreational and commercial drone operations with weird interpretations of recreational flyers not being allowed to fly above a forest if the trees are taller than 400' because that would exceed their 400' AGL restriction. Oh no, you'd need a Part 107 commercial permit for that...


I tried that, but I can only find references to "structures" within CFR Part 77. I was just curious if there's actually an official legal definition. In the USA, recreational flyers can fly over a 400' tall hilltop, but not over a 400' "structure". Hmmmm ?

I don't know if it's in CFR Part 77 but it's in FAA documents. I'll give you a hint... it has to do with "obstacles"