400' AGL over natural feature/"structure"

[Captain Cripple]

Greetings. I'm new here. Howdy.

I've spent real time trying to get a handle on this issue, but definitiveness is elusive.

I've done some photo studies and fun flying at a remote monadnock (there's perhaps yer new word for the day) that offers wonderful opportunities for both. I plan to return.

It seems clear how the 400' AGL limit works with structures in unrestricted airspace - one can operate up to 400' above the highest point of a structure within 400' horizontally of it under Part 107. When LAANC approval is required, that does not apply without a waiver - it's 400' (or whatever) AGL and that's that. The top of the skyscraper might just have to go unsurveyed.

But what if the "structure" is a massive hunk o' rock with both sheer and sloping sides out in the middle of nowhere? Let's use Devil's Tower, WY as an example even tho ya can't fly there on NPS turf.

Is it a structure? Could one, were it not specifically disallowed by The Man as with DT, engage the summit up to 399' above it? And do some dives well in excess of 400' down the face? It seems the answer would be a big YES, but the FAA doesn't have a definitive definition of a structure I can find and opinions on this specific issue are few and conflicting.

It would seem that, were one not allowed to fly over an unrestricted summit, that someone driving a truck to a fire lookout, or even mountain climbers and skiers, would also be a threat to air safety.

I've seen claims that what matters is the 400' directly under the aircraft, but, what of that whole structures thing? I can operate 399' over a tall building with vertical sides 'cuz it's a structure, but not over, say, a 1583' rock that, while sheer in places, is still not quite vertical???

What if I went up a face with a sloping route, over the summit, then a heart-pounding four digit (in feet) dive back to ground level (well, a bit above it is preferred) within (well within, actually, LOL) 400 horizontal feet of the rock? Would that violate the letter of the law? At what point? Immediately when passing the edge of over the sheer drop?

Yes, it's a bit complicated. Thanks for your time.

 

[mavic3usa]

I don't believe there is a question about whether Devil's Tower is a structure/manmade. Your drone can get there without entering the NPS:

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[Felix le Chat]

Greetings. I'm new here. Howdy.

I've spent real time trying to get a handle on this issue, but definitiveness is elusive.

I've done some photo studies and fun flying at a remote monadnock (there's perhaps yer new word for the day) that offers wonderful opportunities for both. I plan to return.

It seems clear how the 400' AGL limit works with structures in unrestricted airspace - one can operate up to 400' above the highest point of a structure within 400' horizontally of it under Part 107. When LAANC approval is required, that does not apply without a waiver - it's 400' (or whatever) AGL and that's that. The top of the skyscraper might just have to go unsurveyed.

But what if the "structure" is a massive hunk o' rock with both sheer and sloping sides out in the middle of nowhere? Let's use Devil's Tower, WY as an example even tho ya can't fly there on NPS turf.

Is it a structure? Could one, were it not specifically disallowed by The Man as with DT, engage the summit up to 399' above it? And do some dives well in excess of 400' down the face? It seems the answer would be a big YES, but the FAA doesn't have a definitive definition of a structure I can find and opinions on this specific issue are few and conflicting.

It would seem that, were one not allowed to fly over an unrestricted summit, that someone driving a truck to a fire lookout, or even mountain climbers and skiers, would also be a threat to air safety.

I've seen claims that what matters is the 400' directly under the aircraft, but, what of that whole structures thing? I can operate 399' over a tall building with vertical sides 'cuz it's a structure, but not over, say, a 1583' rock that, while sheer in places, is still not quite vertical???

What if I went up a face with a sloping route, over the summit, then a heart-pounding four digit (in feet) dive back to ground level (well, a bit above it is preferred) within (well within, actually, LOL) 400 horizontal feet of the rock? Would that violate the letter of the law? At what point? Immediately when passing the edge of over the sheer drop?

Yes, it's a bit complicated. Thanks for your time.

A structure is something constructed. The top of a Mesa or peak is ground level if you're standing on it. 400' AGL applies. Climb to 400' and fly over the edge and your legal flight becomes technically illegal whether it's sloping or not.

 

[AMann]

I am in the US, and was also confused by this as well and my questions were answered as follows:

As long as you are within 400 feet near (laterally or above) a building or hill, including mountains, Devils Tower or table top mesas, you can fly up to 400’ above its highest point as long as you are within 400’ distance from its side or top.

Also keep in mind that as controlled airspace follows mean sea level (msl), if a building or hill height extends within 400’ from or into the base of controlled airspace above it , you are limited how high above either of them you can fly by the base of the controlled airspace unless you have clearance.

 

[ExUmbra.Solutions]

I think it would help your question to understand where the 400 foot rule comes from. I find that Part 107 and recreational pilots who don’t come from a manned aviation background don’t always grasp the intent and the underlying logic of these and it can help when deciding both what is legal but also what is right within the intent when the answer isn’t so black and white.

Manned aviation is prohibited from flying below 500 feet when over any populated area or any terrain (excluding water). The intent of the 400 foot rule is to ensure that if you follow the rules and a fixed wing pilot (notice rotary tends to do their own thing and often violates some of the flight rules you expect them to follow) follows their rules than you will always have separation.

If you are inspecting a 1000 foot tall broadcast tower you can fly up to 1400 all around it because a manned aviation pilot cannot be below 500 feet and within 500 feet of it. When you mention natural terrain features the same logic applies. As long as you are within 400 feet of its edges and 400 feet of its highest point you are both legal and theoretically safe.

A few caveats to this… rotary wing traffic can often fly much lower and in unpredictable areas so be aware when in an urban environment that legal and safe may be two different things. Some heavy air tour areas have exceptions to this such as the Grand Canyon tourist corridor for manned aviation. And, it is a legal gray area to fly in close proximity to some of these taller structures if you aren’t doing so with their permission. Yes, you are in the clear for airspace but as I said it is a gray area if you are flying around a broadcast tower or building and they make an argument that you have either violated privacy laws or may inadvertently cause harm to their infrastructure.

 

[mavic3usa]

I think it would help your question to understand where the 400 foot rule comes from. I find that Part 107 and recreational pilots who don’t come from a manned aviation background don’t always grasp the intent and the underlying logic of these and it can help when deciding both what is legal but also what is right within the intent when the answer isn’t so black and white.

Manned aviation is prohibited from flying below 500 feet when over any populated area or any terrain (excluding water). The intent of the 400 foot rule is to ensure that if you follow the rules and a fixed wing pilot (notice rotary tends to do their own thing and often violates some of the flight rules you expect them to follow) follows their rules than you will always have separation.

If you are inspecting a 1000 foot tall broadcast tower you can fly up to 1400 all around it because a manned aviation pilot cannot be below 500 feet and within 500 feet of it. When you mention natural terrain features the same logic applies. As long as you are within 400 feet of its edges and 400 feet of its highest point you are both legal and theoretically safe.

A few caveats to this… rotary wing traffic can often fly much lower and in unpredictable areas so be aware when in an urban environment that legal and safe may be two different things. Some heavy air tour areas have exceptions to this such as the Grand Canyon tourist corridor for manned aviation. And, it is a legal gray area to fly in close proximity to some of these taller structures if you aren’t doing so with their permission. Yes, you are in the clear for airspace but as I said it is a gray area if you are flying around a broadcast tower or building and they make an argument that you have either violated privacy laws or may inadvertently cause harm to their infrastructure.

The only reason I can think of why US recreational pilots may not need a greater understanding of this is because they are no permitted to fly higher than 400 AGL regardless the height of the structure or where it is located (controlled airspace or not). When I reach a structure that is >400 AGL then I have to go around it instead of over it.

 

[MS Coast]

I am in the US, and was also confused by this as well and my questions were answered as follows:

As long as you are within 400 feet near (laterally or above) a building or hill, including mountains, Devils Tower or table top mesas, you can fly up to 400’ above its highest point as long as you are within 400’ distance from its side or top.

Here's my understanding, from what I remember of the Part 107 training and other discussions here.

• A Part 107 certificate allows you to fly up to 400' directly above a structure and within 400' laterally from the structure. That allowance doesn't apply to landforms; they aren't structures. It also is not applicable within controlled airspace under a LAANC authorization.
  
  
• The 400' altitude limit is referenced to the ground immediately below the drone. There is no allowance for exceeding 400' AGL when within 400' of another landform.

 

[AMann]

The image below explains the rule better (from the FAA) when I asked them the same question. Essentially for pilots in the US, if you fly beyond the edge of a cliff on a tall hill or mountain, and only if the drone is still within 400’ of it in any direction (white arrows), you can fly over 400’ AGL from the ground directly below the drone even though it may be more than 400’ below the drone (blue dashed lines). You just can’t be higher than 400’ from the top or further than 400’ from any of the sides of the hill. It’s the same for part 107 pilots when flying around buildings or above them.

 

[Meta4]

But what if the "structure" is a massive hunk o' rock ...
....
Yes, it's a bit complicated.

It's not complicated when you understand the meaning of the word structure. which was pointed out in post #3.

 

[MS Coast]

The image below explains the rule better (from the FAA) when I asked them the same question. Essentially for pilots in the US, if you fly beyond the edge of a cliff on a tall hill or mountain, and only if the drone is still within 400’ of it in any direction (white arrows), you can fly over 400’ AGL from the ground directly below the drone even though it may be more than 400’ below the drone (blue dashed lines). You just can’t be higher than 400’ from the top or further than 400’ from any of the sides of the hill. It’s the same for part 107 pilots when flying around buildings or above them.

that figure applies to the United Kingdom. Note the reference to Article 94A, which is not an FAA document.

Did the FAA person you dealt with provide that as an explanation of the rule in the US? To my knowledge, the FAA regulations define the 400' AGL limit as the distance to the ground directly below the drone.

Per the UK's Civil Aviation Authority (Scroll down to page 3.): https://www.caa.co.uk/publication/download/18227

 

[AMann]

View attachment 181277

that figure applies to the United Kingdom. Note the reference to Article 94A, which is not an FAA document.

Did the FAA person you dealt with provide that as an explanation of the rule in the US? To my knowledge, the FAA regulations define the 400' AGL limit as the distance to the ground directly below the drone.

Per the UK's Civil Aviation Authority (Scroll down to page 3.): https://www.caa.co.uk/publication/download/18227

It was used as a reference only- perhaps this would’ve been a better image?


So if the distance from the sides doesn’t count in the US, how can one legally fly up to or above the top of a vertical tower , building or cliff if it’s over 400’ tall? Take Notch Peak in Utah for example, one side of it is made up of two vertical cliff faces separated by a narrow bench. One of the vertical faces is about 1,500 feet high, and the other is 700 feet high, thus both together make a nearly vertical cliff face over 2,200 feet tall, the tallest in North America. So if the ruling is for height AGL below the drone, I see that one could only legally fly up to the summit only on the sloped sides while maintaining up to 400’ directly above the terrain below the drone all the way up the sloped sides, but not on the vertical cliff face? Correct? If so, I was told the wrong thing regarding cliffs.

 

[MS Coast]

It was used as a reference only- perhaps this would’ve been a better image?

Yes, that's accurate for the US.

View attachment 181282

So if the distance from the sides doesn’t count in the US, how can one legally fly up to or above the top of a vertical tower , building or cliff if it’s over 400’ tall?

Regarding towers, there's no problem for a pilot with a Part 107 certificate. The drone can fly up to 400' above a tower as long as the it remains within 400' of the tower. Recreational pilots are not allowed to fly more than 400' AGL, so flight over the tower is off limits.

Take Notch Peak in Utah for example, one side of it is made up of two vertical cliff faces separated by a narrow bench. One of the vertical faces is about 1,500 feet high, and the other is 700 feet high, thus both together make a nearly vertical cliff face over 2,200 feet tall, the tallest in North America. So if the ruling is for height AGL below the drone, I see that one could only legally fly up to the summit only on the sloped sides while maintaining up to 400’ directly above the terrain below the drone all the way up the sloped sides, but not on the vertical cliff face? Correct? If so, I was told the wrong thing regarding cliffs.

For any absolutely vertical landform that rises more than 400' above the immediately adjacent ground, it would not be legal to fly up it. In the real world, I suspect there aren't many examples of such situations.

 

[saul01]

Greetings. I'm new here. Howdy.

I've spent real time trying to get a handle on this issue, but definitiveness is elusive.

I've done some photo studies and fun flying at a remote monadnock (there's perhaps yer new word for the day) that offers wonderful opportunities for both. I plan to return.

It seems clear how the 400' AGL limit works with structures in unrestricted airspace - one can operate up to 400' above the highest point of a structure within 400' horizontally of it under Part 107. When LAANC approval is required, that does not apply without a waiver - it's 400' (or whatever) AGL and that's that. The top of the skyscraper might just have to go unsurveyed.

But what if the "structure" is a massive hunk o' rock with both sheer and sloping sides out in the middle of nowhere? Let's use Devil's Tower, WY as an example even tho ya can't fly there on NPS turf.

Is it a structure? Could one, were it not specifically disallowed by The Man as with DT, engage the summit up to 399' above it? And do some dives well in excess of 400' down the face? It seems the answer would be a big YES, but the FAA doesn't have a definitive definition of a structure I can find and opinions on this specific issue are few and conflicting.

It would seem that, were one not allowed to fly over an unrestricted summit, that someone driving a truck to a fire lookout, or even mountain climbers and skiers, would also be a threat to air safety.

I've seen claims that what matters is the 400' directly under the aircraft, but, what of that whole structures thing? I can operate 399' over a tall building with vertical sides 'cuz it's a structure, but not over, say, a 1583' rock that, while sheer in places, is still not quite vertical???

What if I went up a face with a sloping route, over the summit, then a heart-pounding four digit (in feet) dive back to ground level (well, a bit above it is preferred) within (well within, actually, LOL) 400 horizontal feet of the rock? Would that violate the letter of the law? At what point? Immediately when passing the edge of over the sheer drop?
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Yes, it's a bit complicated. Thanks for your time.

Welcome! That’s a fascinating question, and you're right—FAA guidance on defining "structures" is murky. Given Part 107's wording, your interpretation seems reasonable, but an official FAA ruling would clarify things. Safe flying!

 

[MS Coast]

Welcome! That’s a fascinating question, and you're right—FAA guidance on defining "structures" is murky. Given Part 107's wording, your interpretation seems reasonable, but an official FAA ruling would clarify things. Safe flying!

Where is the murk? Landforms are not structures.

What aspect of the Part 107 regulations regarding flights over and near structures needs clarification?

 

[Captain Cripple]

I don't believe there is a question about whether Devil's Tower is a structure/manmade. Your drone can get there without entering the NPS:

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Hi. Indeed, not a lot of confusion as to whether DT is manmade, but there seems to be a bit of fuzz around whether such a thing can be a structure, which, at least in some definitions, isn't necessarily manmade.

If something shows on a sectional chart, I'm inclined to think I can legally fly up to 400' above its peak within 400' laterally of it.

The intent seems to be to foster aviation safety and manned craft must remain over 400' from the object/structure/thingeee, so it seems acceptable to operate a UAV in the 400' "half bubble" around the apex of the, uh, thingee.

For sure, fine footage of Devils (the USGS seems to be at odds with apostrophes) Tower can be had from operations controlled from just outside the NPS line.

The plot thickens - what if the structure is a bridge, such as Rio Grande (or New River) Gorge Bridge? It's most definitely a structure, is well over 2 x 400' long and well over 400' above the ground.

If one is paralleling it 390' from the edge, 390' above the deck level, and while in the middle of the parallel more than 400' from either end, they should be legal despite there being about 600' of empty air under the bridge and about 1000' of empty air under the UAV, right?

And what of flying under the bridge? Does the "half bubble" extend under the bridge, too, or does the river now become the base for the yardstick? 400' under the bridge? 400' above the river/rocks? Both?

Hopefully there wouldn't be a John Lappo "military flyunder" type thing going on while operating beneath the bridge

Is this guy, assuming he's Part 107, legal in terms of the 400/AGL thing? Regardless, I see some issues with 107.23 hazardous operation, given that people recreate, work, and study at the river far below. Shooting that one gap across is one thing, but that ride thru the bridge structure seems rather....sketchy. Link cued up:

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[Captain Cripple]

A structure is something constructed. The top of a Mesa or peak is ground level if you're standing on it. 400' AGL applies. Climb to 400' and fly over the edge and your legal flight becomes technically illegal whether it's sloping or not.

Hi. Cool moniker.

I'm having a hard time finding a definitive definition of the term according to the FAA.

If I'm at the top of a 500' mesa with sloping sides, I can't fly over the edge and follow the slope down even if the near sloping side is far less than 400' beneath the aircraft?

That doesn't seem quite right to me, but still can't find a definitive answer in the FAA's "bag of tricks" (couldn't resist, I grew up watching FtC).

 

[Captain Cripple]

As long as you are within 400 feet near (laterally or above) a building or hill, including mountains, Devils Tower or table top mesas, you can fly up to 400’ above its highest point as long as you are within 400’ distance from its side or top.

Also keep in mind that as controlled airspace follows mean sea level (msl), if a building or hill height extends within 400’ from or into the base of controlled airspace above it , you are limited how high above either of them you can fly by the base of the controlled airspace unless you have clearance.

Good morning. Thanks for the well-crafted post and the controlled airspace clarification.

That seems to be how I interpret the rule.

What's your take on the bridge issue I've now dragged into this matter in post #15?

Cheers!

 

[Captain Cripple]

It's not complicated when you understand the meaning of the word structure. which was pointed out in post #3.

That's what I initially thought, but the lack of a definitive definition of "structure" is an issue. Constructed by whom or what?

Devils Tower can be considered, at least in some aspects, a structure. This paragraph is a structure, as are a sheet of paper and our skeletons.

It's what the FAA claims a structure to be that is the sticking point here. I can't fathom a reason why a rock spire would be treated differently than a building or broadcast tower.

 

[MS Coast]

Good morning. Thanks for the well-crafted post and the controlled airspace clarification.

"As long as you are within 400 feet near (laterally or above) a building or hill, including mountains, Devils Tower or table top mesas, you can fly up to 400’ above its highest point as long as you are within 400’ distance from its side or top."

That's correct in the United Kingdom, but not in the United States. See post #10.

 

[Captain Cripple]

View attachment 181277

that figure applies to the United Kingdom. Note the reference to Article 94A, which is not an FAA document.

Did the FAA person you dealt with provide that as an explanation of the rule in the US? To my knowledge, the FAA regulations define the 400' AGL limit as the distance to the ground directly below the drone.

Per the UK's Civil Aviation Authority (Scroll down to page 3.): https://www.caa.co.uk/publication/download/18227

Howdy. I like your name and byline. A cajun friend actually has "LA as in Louisiana" in his siggy on another board. Abbreviations that are also words can cause confusion, yes. LOLZ.

That diagram is how I interpret the rule, but the "directly under the drone" thing is quite at odds with the building/structure allowance, so the directly under part seems to apply to TRUST etc. flights while the 400' "bubble" above and to the sides (and what of below, as explained in the bridge thing I've added in #15) of the structure/landform under 107 is a different story.

Apparently. LOL.