400 ft ATO -- But higher AGL?

[Zbip57]

Trees are not Structures. . .

Trees are not structures, but sometimes structures are in trees.



And, trees are not structures, but sometimes structures are trees.



It's all very simple.

 

[MS Coast]

It would only be extremely simple if the rules treated every hazardous obstacle the same way. But it doesn't.

Recreational pilots cannot fly over trees that are taller than 400'. Neither can Part 107 pilots! They're only allowed to fly higher over tall "structures", and as BigAl07 points out, trees are not structures.

Everyone is allowed to fly 400' higher than any terrain "ground" feature composed of natural earth and rocks, since you're always allowed to fly up to 400' above "ground". So why is ground treated differently than structures? And why aren't trees considered as "ground"? Why do you first need to figure out whether a particular obstacle of earth/rocks is a natural terrain "ground" feature versus a man-made "structure" of earth/rocks? They're each equally obstacles in the way of aviation.

I posted several images a couple of days ago illustrating these questions over in another thread:
mavicpilots.com/threads/why-1400-ft-max-altitude.124266/page-4#post-1408241



I can think of one exception.

What exactly is the "ground" when one refers to AGL? Structures are not ground, and trees are not structures, and trees are also not ground. So trees just don't exist at all, even though they're an obvious hazard to aviation.

So when is "ground" not actually a natural terrain feature composed of earth or rocks (not trees), and definitely never to be confused with un-natural rock/earth man-made "structure"?

The exception is that 400' AGL is not always measured from solid ground. It's also frequently measured from the top surface of any body of water, rather than from the solid ground at the lake's bottom. Trees are not structures and not ground. Water is not a structure, but it is ground. Okay.

Here's another example where the 400' AGL, with no exceptions, for Recreational Pilots is neither extremely simple nor obvious.

Lets pick an obvious "obstacle" like the Hoover Dam. NOTE: You're not actually allowed to fly over the Hoover Dam. It's a strict NFZ. Flying a Chinese drone to take surveillance images over such a vulnerable "structure" is a threat to Homeland Security. Of course any tourists, even Chinese tourists, are instead welcome to drive their car along the top of the dam, and stop at the visitor centre to take a tour of the power plant and snap as many photos as they like. You just can't do it using a drone, because... Well, um, just because.

Solely for the purpose of this example, assume that Recreational Pilots are allowed to fly over the Hoover Dam. Below is a cross sectional diagram. How high would you be allowed to fly here?

The dam itself is 726' high, presumably measured from the "ground" up. So, if you're never allowed to fly higher than 400' above "ground", you'd never be allowed to fly over this dam.

But you're in luck, because apparently one can measure AGL relative to the top of the water's surface, not actually from the "ground". Don't ignore the fact that the water level in this reservoir can fluctuate quite dramatically. But assume that, arriving from upstream at a height not exceeding 400' AGL, you can clear the top of the dam.

Bit wait! You still cannot cross over the top of the dam! Remember that dam is a "structure", not "ground". That 726' tall stucture is taller than 400' AGL, therefor Recreational Pilots CANNOT fly over it, (even if it wasn't a NFZ).

What about if you approach the dam from downstream? You can only fly as high as 400' above the water's surface, nowhere near high enough to clear the dam.

And, it gets worse. Right at the point where the water's surface touches the dam's face, you'd must descend. You're only allowed to fly 400' above "ground" (or water), but only Part 107 pilots are allowed to fly an additional 400' above a "structure". The moment you cross leave the surface of the water and are now over the surface of the "structure" of the dam, Recreational pilots are required to descend to a point no higher than 400" above "ground" (not above structure). And good luck figuring out how far that actual unseen "ground" is buried beneath all that concrete "structure".

It's all "extremely simple". Ya right.

Why do we need to distinguish between "ground (including water)" versus "structures", with different rules depending on which is which. Why not have one consistent rule for 400' over any hazardous obstacle?

View attachment 146590

I'm unable to address this issue with the zeal and diligence you apply, and I think the last breath of life has been beaten out of this dead horse. But I will offer three comments. (As humor!)

• "Recreational pilots cannot fly over trees that are taller than 400'. Neither can Part 107 pilots!
  This would be a better example of onerous overreach by federal regulatory agencies if examples of 400' trees were provided. I find the inability to operate above nonexistent trees to be no limitation to my flying. [Note: edited to correct typo - 700 to 400.]
  
  
• I suspect the real reason for the prohibition of flying over the Hoover Dam is to hide the bothersome paradox you've found in the 400' AGL regulation with respect to tall dams. It has nothing to do with national security.
  
  
• I find nothing in the regulations that prohibit flying underwater in the submerged portions of the national airspace.
  

I maintain that the 400'AGL rule is still extremely simple in the real world.

 

[Yorkshire_Pud]

I find nothing in the regulations that prohibit flying underwater in the submerged portions of the national airspace.

in humour

but you might in a dictionary, I don't think even Manta Rays fly under water surely they swin?????

 

[Zbip57]

I maintain that the 400'AGL rule is still extremely simple in the real world.

Yet, another thing to consider. The FAA rules might be considered extremely simple (ha!), however there is considerable international participation in this forum and, of course, the rules are completely different in other countries.

Thankfully, most countries agree on the relatively simple 400' AGL limit for drones. But there are many different confusing interpretations of how the extra height allowance over "structures" is to be handled.

Here in Canada drones are allowed up to 400' AGL, yet daylight VFR flights of manned aircraft are permitted to no less than 300 feet AGL or at a horizontal distance of less than 300 feet from "any obstacle". See CARS 703.27(b) There's a potential overlap of 100'. Why?

And, here in Canada, everyone is allowed to fly drones over structures taller than 400', regardless of intent (recreational vs commercial). There's no difference in the applicability of the rules, except based on weight of the drone and where it's being flown. For drones weighing between 250g-25kg, pilots holding a Basic certificate cannot fly within any controlled airspace. For that you need an Advanced certificate. It doesn't matter if it's for recreational fun or commercial inspection. Makes no difference whatsoever.

Except for taking into account controlled airspace, any Basic or Advanced pilot is allowed to fly up to 400' AGL, and an additional 100 feet over "any building or structure" taller than 400', as long as you stay within 200 feet horizontally. See CARS 901.25

Then there's the UK, for which "Ian in London" says the rule is you can only fly 15m (49 feet) higher than a 400' structure, as long as you stay horizontally within 50m (164 feet) of the structure.

Ian says their rules are "remarkably clear".

Wouldn't it be a whole lot simpler if everyone could agree on a 100' buffer separation with something like this.

• Manned aircraft should stay 500' away from any obstacle, and
• Unmanned aircraft should fly no higher than 400' above any obstacle while staying within 400' distance of any obstacle that's taller than 400'.

 

[Yorkshire_Pud]

Also our 400ft rule is not AGL but rather within 400ft of the closest ground which means we can climb 400ft+ vertical cliffs providing the drone is within 400ft of the cliff face i.e. a 400ft long string attached to the drone must be able to touch the ground somewhere.

 

[Trackerputnam]

If I am inspecting a cell phone tower, it says I can fly 400’ above that tower! Yes, 107. And a certain distance away, can’t remember that now, but that puts me well above 400’ of the ground. is that right?

 

[MS Coast]

If I am inspecting a cell phone tower, it says I can fly 400’ above that tower! Yes, 107. And a certain distance away, can’t remember that now, but that puts me well above 400’ of the ground. is that right?

If Part 107, 400' above the obstruction if within 400' horizontally. So max altitude is 400 + height of obstruction.

 

[z28lt1]

If Part 107, 400' above the obstruction if within 400' horizontally. So max altitude is 400 + height of obstruction.

All true, except I'll add that as long as the structure is not in B ,C, D or E2 airspace OR if the 400 foot above puts you in B,C or D.

In other words this is true as long as you remain in uncontrolled (or some specific E) airspace or you have a waiver.

 

[Chaosrider]

I explained how you can do mapping entirely for free in this post:
mavicpilots.com/threads/drone-mapping.124355/#post-1407306

There are limitations though when using something like a Mini versus more capable drones.

Many people use and recommend DroneDeploy, but according to their website they don't support my Mini or my Phantom 3 Pro.

Cool.

It's currently snowing with high winds so...not today!

Thx,

MM

 

[Camino Ken]

I wouldn't use that architecture at all to get AGL altitude.

I'd integrate the existing GPS position data that the drone already has, with a terrain data base that has the MSL elevations for the GPS locations in the region in question.

Then it's just math.

Take the MSL altitude of the take-off point, add the ATO altitude that the drone displays already, subtract the database-known MSL altitude of the current GPS location directly under the drone, and Presto!

AGL altitude.

As precise as radar? No.

Good enough? Absolutely!

There would be zero or virtually zero new hardware involved. Maybe a memory/processor chip.

I expect the biggest per unit cost would be the licensing fee for the terrain database.

Conceptually, it's not hard. I don't even think the coding would be that hard. I think providing this would seriously improve compliance with the 400 ft AGL rule. If Ms Fly yelled at you when you got to 400 ft AGL, rather than 400 ft ATO as she does now, it would matter more to people. Even an actual flight control hold at that point, which should be dismissible, shouldn't be that hard.

Of course, if you're a flatland flier, none of this matters...



TCS

If I’m not mistaken, Litchi has a function/option to program a flight “Above Ground Level”. I have never used it and not sure how accurate it is.

 

[dronerdave]

View attachment 146603
I maintain that the 400'AGL rule is still extremely simple in the real world.

I agree as you simple are allowed to fly max 400' above the water or terrain/ground. Basically the (dam) outcome is no different than a sheer vertical cliff. While I'd like to see a rec flight be able to be regulated similar to 107 as far as operating 400' from a structure, the rules don't allow it. I deal with it.

There seems to be two camps in this and many rules arguments. One camp wants to find a loophole to avoid flying in compliance and the other camp accepting the rules and flying in compliance. Sorry but that is what I see a lot. Not that I wouldn't suggest lobbying to change the rules, but as I said I just deal with current regs. The tree house spin humors me.

 

[Zbip57]

If I’m not mistaken, Litchi has a function/option to program a flight “Above Ground Level”. I have never used it and not sure how accurate it is.

Yup, and Litchi functions the same way. You tell it to plot its waypoints to maintain a desired constant height above ground, say a constant 50' AGL. The app plots the desired waypoints, compares those GPS locations to an internal database of MSL elevations (like Google Earth), then calculates the difference in height between that GPS location and your takeoff location, and adds the desired 50'. Presto. Upload all those waypoints, including the calculated height, to the drone and send it on its way.

The drone itself still has no idea how high (AGL) it is above any particular point that it's flying over. All of its waypoints heights are still referenced back relative to the zero height of its recorded takeoff location. It just knows how much it needs to climb or descend to reach the next waypoint.

But there could still be a tall tree in its path...

 

[Zbip57]

"Recreational pilots cannot fly over trees that are taller than 400'. Neither can Part 107 pilots!
This would be a better example of onerous overreach by federal regulatory agencies if examples of 700' trees were provided. I find the inability to operate above nonexistent trees to be no limitation to my flying.

Why 700' trees? Or did you actually mean to say 400' trees?

According to Wikipedia, the tallest tree on record is 380' tall. That leaves a mere 20' margin over top of it, just enough room to squeeze a drone through. That's for BOTH recreational and Part 107.

But, instead of a tree, what if that was an equally tall 380' tower?

Recreational pilots could launch from the top of the tower, and fly off in any direction, but be restricted to climbing no more than an additional 20' higher than the tower (400' AGL max).

Part 107 pilots are also allowed to fly as far they want in any direction no higher than 20' above the tower, PLUS they can fly an additional 400' higher as long as they stay within a 400' horizontal radius of the tower.

Why are Part 107 pilots trusted to fly an additional 400' over the tower, but only 20' over a tree of the same height? "Because them's the rules!"

Nope. It's because manned aircraft are required to avoid "structures", but are allowed to skim treetops. Both are "obstacles" presenting similar hazards to aircraft, no?

One of these rules makes no sense.

 

[z28lt1]

Why 700' trees? Or did you actually mean to say 400' trees?

According to Wikipedia, the tallest tree on record is 380' tall. That leaves a mere 20' margin over top of it, just enough room to squeeze a drone through. That's for BOTH recreational and Part 107.

But, instead of a tree, what if that was an equally tall 380' tower?

Recreational pilots could launch from the top of the tower, and fly off in any direction, but be restricted to climbing no more than an additional 20' higher than the tower (400' AGL max).

Part 107 pilots are also allowed to fly as far they want in any direction no higher than 20' above the tower, PLUS they can fly an additional 400' higher as long as they stay within a 400' horizontal radius of the tower.

Why are Part 107 pilots trusted to fly an additional 400' over the tower, but only 20' over a tree of the same height? "Because them's the rules!"

Nope. It's because manned aircraft are required to avoid "structures", but are allowed to skim treetops. Both are "obstacles" presenting similar hazards to aircraft, no?

One of these rules makes no sense.

I have no inside information on the decision making of the FAA, but putting two and two together (or 1 and 2):

1. Using drones to inspect towers is a valid and very likely commercial use of drones that a Part 107 flier might need to do.

2. Part 107 fliers have demonstrated knowledge that they understand the rules around towers, understand airspace classification that may still restrict their height at those towers, understand runway patterns to know where aircraft might be in the area of a tower, understand radio frequencies to listen in on traffic patterns if need be, understand rules around flying near clouds, etc. that a Recreational flyer might not know.

So, there is a commercial need to do something, and training given to make that something less risky, so the FAA allowed it for one group and not the other.

And while I don't disagree that in general the risk might be pretty low for a recreational pilot as well as manned aircraft are going to go around buzzing structures, the additional altitude certainly poses more risk than the simple 400 feet above AGL, and it is very possible that 400 feet above the top of the tower is in restricted airspace while the bottom of the tower is not which is something a rec pilot might not be aware of at all.

 

[Zbip57]

Basically the (dam) outcome is no different than a sheer vertical cliff.

That's my whole point. They should be no different.

But the dam is a structure, and a cliff is terrain. Different rules apply to each, despite their obvious similarity.

If the dam was instead a cliff of natural terrain, you would be allowed to fly to a height of 400' above it. Approaching from upstream, you can fly 400' above the water, then a small step up onto the dam, crossing even as high as another 400' over the top of the dam, then descending the downstream slope while always remaining no more than 400' vertically above the steeply downward sloping surface of the concrete.

But, because the dam is a "structure" taller than 400', it's a totally different kettle of fish. Recreational pilots cannot fly over any structure that tall.

There seems to be two camps in this and many rules arguments. One camp wants to find a loophole to avoid flying in compliance and the other camp accepting the rules and flying in compliance. Sorry but that is what I see a lot. Not that I wouldn't suggest lobbying to change the rules, but as I said I just deal with current regs. The tree house spin humors me.

There is a third camp, to which I belong. I have no intention or desire to ever fly over Hoover Dam, and I'm definitely not seeking loopholes to avoid flying in compliance.

I just don't like poorly worded regulations that are either so confusing that people won't bother trying to understand them, or so onerous that people will try to find loopholes or deliberately ignore them.

You just need to search this forum for plentiful evidence that this 400' AGL rule, plus 400' over tall structures, remains confusing, misunderstood, and frequently debated. And this forum is fortunate to have so many truly intelligent and helpful people visiting it. Just imagine how many more people are out there who just recently got their first drone for Christmas/Birthday/etc, who don't even know that these regulations exist, haven't yet discovered this forum, and see no reasonable explanation for why they shouldn't be allowed to fly off the edge of a 400' vertical cliff or from their apartment's balcony.

 

[dronerdave]

But, because the dam is a "structure" taller than 400', it's a totally different kettle of fish. Recreational pilots cannot fly over any structure that tall.

If the water level is 100' below the top of the dam, then you are saying I can't fly over the top of the dam? I'm thinking I can fly over the dam until I reach the side where it drops vertically down into the canyon where I must stop. Maybe I'm wrong. As I understand it, from the downstream side I can only fly to the face of the dam and then only 400' higher from the water surface.

 

[Tomk_]

Believe it or not, the FAR/AIM tries to simplify the rules. It is not designed to have a specific rule for every situation that someone can come up with playing "what-if" games. Anyone can see that using AGL is appropriate for drones as it is the same term and usage for manned aircraft - actually for everything covered by the FAR/AIM. The 400 ft rule works nicely with manned aircraft's 500 ft rule. The problem is the exceptions that are not all spelled out out. Instead we revert to right-of-way and see and avoid.

Doesn't anyone else think that the number of threads we have had on this forum where members endeavor to "prove" that the regulations are nonsensical by setting up straw men just tends to make all drone pilots look a little silly? Do any of you think that there are manned flight forums full of pilots arguing that it's not fair that they can fly closer to trees than they can cell towers or buildings. Or that they shouldn't be required to be IFR certified before allowed to fly in clouds because if they weren't supposed to fly in clouds that the plane manufacturers wouldn't have built them able to do that?

Anyone that has dealt with the FAA more than a few minutes realizes that they don't see their job as sky police. They are not out looking for people that break the rules. They see their job as all about safety. If they don't see a safety problem, they don't want to get involved. If they see something that they think is unsafe...the rules give them enough options to remove the offender from the sky. It's really that simple. If you want to fly of the edge of a 500 ft shear cliff, no one is going to stop you are even harass you - as long as their is no incident - even though it is not legal. However, if there is an incident - you rolled the dice and took your chances and you have earned the consequences.

"There is none so blind as those that will not see." ~ John Heywood (1546)

 

[MS Coast]

Believe it or not, the FAR/AIM tries to simplify the rules. It is not designed to have a specific rule for every situation that someone can come up with playing "what-if" games. Anyone can see that using AGL is appropriate for drones as it is the same term and usage for manned aircraft - actually for everything covered by the FAR/AIM. The 400 ft rule works nicely with manned aircraft's 500 ft rule. The problem is the exceptions that are not all spelled out out. Instead we revert to right-of-way and see and avoid.

Doesn't anyone else think that the number of threads we have had on this forum where members endeavor to "prove" that the regulations are nonsensical by setting up straw men just tends to make all drone pilots look a little silly? Do any of you think that there are manned flight forums full of pilots arguing that it's not fair that they can fly closer to trees than they can cell towers or buildings. Or that they shouldn't be required to be IFR certified before allowed to fly in clouds because if they weren't supposed to fly in clouds that the plane manufacturers wouldn't have built them able to do that?

Anyone that has dealt with the FAA more than a few minutes realizes that they don't see their job as sky police. They are not out looking for people that break the rules. They see their job as all about safety. If they don't see a safety problem, they don't want to get involved. If they see something that they think is unsafe...the rules give them enough options to remove the offender from the sky. It's really that simple. If you want to fly of the edge of a 500 ft shear cliff, no one is going to stop you are even harass you - as long as their is no incident - even though it is not legal. However, if there is an incident - you rolled the dice and took your chances and you have earned the consequences.

"There is none so blind as those that will not see." ~ John Heywood (1546)

Amen.

 

[Zbip57]

If the water level is 100' below the top of the dam, then you are saying I can't fly over the top of the dam?

You are allowed to fly as high as 400' AGL measured from the water's surface on the upstream side of the dam. But only as long as you remain over the water.

From the water to the top of your dam is a mere 100', so it looks like you would still be well under the 400' ceiling if flying over the dam. If the dam was a natural terrain feature, you would be allowed to ascend those initial 100' from the water to the top surface of the dam, plus as much as another 400' more AGL measured starting from the top of the dam.

However, because of the peculiar distinction between terrain and structures, only a Part 107 pilot would be allowed to fly anywhere over the top surface of the dam. The top of your dam is shown as 1000' AGL, not measured from the water's surface, neither from the upstream or downstream side of the dam, but that height is now measured from the "ground" which the dam is standing on. Since recreational flyers are never allowed to fly higher than 400' AGL (ground), that means you cannot fly over this "structure", but Part 107 pilots can fly over such tall structures.

In your diagram the downstream face of the dam is vertical and taller than allowed for recreational flyers. Part 107 pilots are allowed to fly up/down this side as long as they stay within 400' horizontally of the dam's face. Recreational flyers can only ascend vertically as high as 400' from the water's surface, and are not allowed to descend from the top of the much higher dam.

My diagram is different in that the downstream face of the dam is sloped. If that was a natural terrain feature, then any recreational flyer would be allowed to fly all the way up the entire sloped face as long as they stay no higher than 400' vertically of the sloped surface. But they cannot do that if it's a "structure". Recreational pilots can only fly over structures that are less than 400' tall. So they can only fly 400' up that inclined surface, as measured vertically from the "ground" beneath the concrete structure.

 

[Deleted member 93449]

Believe it or not, the FAR/AIM tries to simplify the rules. It is not designed to have a specific rule for every situation that someone can come up with playing "what-if" games. Anyone can see that using AGL is appropriate for drones as it is the same term and usage for manned aircraft - actually for everything covered by the FAR/AIM. The 400 ft rule works nicely with manned aircraft's 500 ft rule. The problem is the exceptions that are not all spelled out out. Instead we revert to right-of-way and see and avoid.

Doesn't anyone else think that the number of threads we have had on this forum where members endeavor to "prove" that the regulations are nonsensical by setting up straw men just tends to make all drone pilots look a little silly? Do any of you think that there are manned flight forums full of pilots arguing that it's not fair that they can fly closer to trees than they can cell towers or buildings. Or that they shouldn't be required to be IFR certified before allowed to fly in clouds because if they weren't supposed to fly in clouds that the plane manufacturers wouldn't have built them able to do that?

Anyone that has dealt with the FAA more than a few minutes realizes that they don't see their job as sky police. They are not out looking for people that break the rules. They see their job as all about safety. If they don't see a safety problem, they don't want to get involved. If they see something that they think is unsafe...the rules give them enough options to remove the offender from the sky. It's really that simple. If you want to fly of the edge of a 500 ft shear cliff, no one is going to stop you are even harass you - as long as their is no incident - even though it is not legal. However, if there is an incident - you rolled the dice and took your chances and you have earned the consequences.

"There is none so blind as those that will not see." ~ John Heywood (1546)

I agree with you to a point but I also don't assume most people that have a question about the restrictions are just looking an excuse to violate regulations.

One of the issues that causes some of the misunderstanding is changes in the rules and the misinformation out there based on those changes. Even now if you search for rules on altitude you find information that mingles part 107 and recreational rules together.

There has been discussion in this thread regarding what constitutes a structure. The dictionary definition of a structure is "the arrangement of and relations between the parts or elements of something complex." It says nothing about man made or naturally occurring.

If you tell someone to go to the source (FAA 44809) they are greeted with this...

FAA 44809

Someone wants to fly a drone in their backyard or hundreds of acres of open farmland or a local park is now required to wade through 44809 and take a test?

Flying drones and RC aircraft have been around for decades. There is near zero risk of injuries or fatalities and yet the rule makers use the what ifs you derided to create a massive new set of regulations. I think the regulators have gone to far in an attempt to solve a problem that doesn't exist and when that happens there is typically a backlash.