400 ft ATO -- But higher AGL?

[Chaosrider]

I can't figure out why AGL is such a difficult term to comprehend as it returns the distance to the ground directly below the aircraft, not at an angle to a cliff. Above ground below the aircraft is so simple.

I agree.

Understanding the term is now what's in question.

Thx,

TCS

 

[Chaosrider]

I think the "ATO" confusion is because if you set an altitude limit in DJI Fly it is above takeoff altitude. But this has no regulatory meaning. DJI may let you fly off the cliff to an area where you are 1000 AGL because the drone does not know about the cliff. But the regulation is 400 AGL at all times, regardless of where you took off.

ATO is all the data you get when you're flying, so it's an important concept.

MM

 

[Chaosrider]

No I'm suggesting you use AGL because that's the only height that matters in terms of regulations.

ATO is NOT an FAA Term and not something you'll see in the regulations. Even in rough/hilly terrain you are giving you Best Guess as to if the aircraft if 400'AGL, 390'AGL, or 410' AGL. There's no reason why you can't fly lower and increase your Margin of Safety in terms of not violating the 400' AGL rule.

The moment you transition away from your takeoff point your altitude is an estimation if you're relying on the on-screen altitude. If there is an incident your real altitude will be determined forensically using your logs and GPS data etc. All that matter is AGL.

I'm not trying to be a pain here, I'm really trying to know what the rule is. I have a memory that Rec pilots have a restriction based on ATO. If that's wrong, then I'll learn something through this.

But it's more than a little weird if the only altitude value that matters, isn't one that you can see on your screen, and the only altitude value you can see on your screen, doesn't matter.

It matters to Ms Fly, of course. She squawks whenever you go over 400 ft ATO. If ATO doesn't matter...then why would she do that?

Maybe it's just a flatlander thing...

Thx,

MM

 

[Kilrah]

But it's more than a little weird if the only altitude value that matters, isn't one that you can see on your screen, and the only altitude value you can see on your screen, doesn't matter.

Aviation regulations are made for aircraft that move far and fast, and for which takeoff altitude thus means nothing at all, AGL altitude will be different within seconds.
Note that most full scale pilots also have no measurement of AGL altitude and have to estimate just like you do, which is probably more difficult than the majority of drone flights where when you're within 500ish m of your takeoff point unless you're at the edge of a cliff ground level isn't going to change much.

 

[Merrill277]

Flying less than 400 ft ATL is alright for flat landers but makes no sense for mountains. If you're at the top of a 4,000 ft mountain you can fly anywhere along the mountain because you're flying below your take off point but if you're at the bottom and take off, you're limited to the 400' ATL rule. See my point?

 

[dronerdave]

Flying less than 400 ft ATL is alright for flat landers but makes no sense for mountains. If you're at the top of a 4,000 ft mountain you can fly anywhere along the mountain because you're flying below your take off point but if you're at the bottom and take off, you're limited to the 400' ATL rule. See my point?

I've never had that problem. All I do is fly along the terrain and stay below about 300 feet above the ground below my drone. That gives me a buffer of safety from violating the 400 foot rule. I can usually avoid trees by looking at my video screen and can aviod other aircraft by keeping in VLOS. How steep the terrain is can pose a problem if there are tall trees on the cliff but overall I never have a problem. The only thing that limits me is the max altitude programmed by DJI of 500 meters or 1640 feet. On a steep cliff it doesn't take too long to hit that limit even if I'm only 50 feet above the deck.

 

[Paint Rock Drones]

This example assumes hard VLOS maintained at all times.

Under this interpretation, if a rec pilot takes off, and climbs to the top of a 1000 ft hill, they're perfectly legal, as long as they are never more than 400 ft AGL?

Is that what you're suggesting?

Thx,

TCS

That sounds right to me. Assuming no other airspace restrictions, VLOS, and not flying over people or moving vehicles, etc., you can fly as high above sea level (ASL) as you want as long as you are within 400 ft. above ground level (AGL). Doesn't matter where you were when the drone took off.

 

[Paint Rock Drones]

ATO is all the data you get when you're flying, so it's an important concept.

MM

I'm not implying anything about whether it is an important concept, and yes, it is the only thing shown on your display. I'm just saying from a regulatory point of view, it is irrelevant. The rules say 400 AGL. The fact that DJI chooses to display "ATO" and provide warnings based on the same does not mean that has any legal relevance. That means especially when you are on uneven terrain you have to plan your flight and maintain VLOS if you want to fly within the rules.

 

[Trackerputnam]

If you are flying over trees, you can be 400’ above those and still be in compliance. If you are inspecting a cell tower, you can be 400’ above that even if it is a 1000’ foot tower! So agl is relative to what’s below you.

 

[Chaosrider]

The FAA actually doesn't recognize Above Take Off as an actual altitude. It's only a thing because manufacturers don't have a way to give you AGL data (at the moment).
Recreational pilots, just like part 107 pilots, are limited to 400 feet AGL at all times. Part 107 pilots do have access to an additional rule that allows them to fly above 400 feet AGL as long as they are in airspace that doesn't require approval, and as long as they are within 400 feet horizontal of a structure.

I think I remember this now. I have my 107.

So, a Rec pilot couldn't take off next to a 400 ft building, and fly 400 ft above it, right?

But how high can you go next to this hypothetical building? If you're, say, 200 ft from the building with your 107, and the building is 400 ft high, you fly to 800 ft AGL/ATO (the two would be the same in this scenario). Can you then fly any higher than that?

I think the answer is "no", but that's part of what I'm trying to sort out in my head.

Thx,

TCS

 

[dronerdave]

If you are flying over trees, you can be 400’ above those and still be in compliance. If you are inspecting a cell tower, you can be 400’ above that even if it is a 1000’ foot tower! So agl is relative to what’s below you.

As I've read it, that is not correct.

It's the ground not trees. Trees are not a man made structure. So if you are flying over a grove of tall redwood trees that measure over 400 feet tall from the ground, you'd be flying out of compliance. If you are inspecting a cell tower you must fly under 107 which allows you to fly within 400' of the man made structure. If you are flying under the recreational bubble, 400'AGL directly below your drone is the max.

 

[Chaosrider]

There is NEVER a case where the legality of flying at a particular point in the air depends on the aircraft's take-off altitude.

The safety or danger of flying at a particular spot in the air doesn't depend on the takeoff altitude. That's why the legality of flying at a particular spot also doesn't depend on the takeoff altitude.

Furthermore, enforcement is simpler if those observing don't have to track the takeoff point of every flying object that is observed in order to know whether or not a violation occurred.

That makes sense to me.

But making sense is no guarantee that it's the actual rule...but it seems like it is in this case.

Thx!

MM

 

[Chaosrider]

Totally wrong

There is no 400 ft ATO rule
No aviation safety authority in the world has any rule relating to altitude above takeoff point.
And it shouldn't take much thought to understand why, but this might help you to understand.

Makes sense.

I had two conflicting versions of the rule in my head, and I asked the question to help sort them out.

Thx,

MM

 

[dronerdave]

I think I remember this now. I have my 107.

So, a Rec pilot couldn't take off next to a 400 ft building, and fly 400 ft above it, right?

But how high can you go next to this hypothetical building? If you're, say, 200 ft from the building with your 107, and the building is 400 ft high, you fly to 800 ft AGL/ATO (the two would be the same in this scenario). Can you then fly any higher than that?

I think the answer is "no", but that's part of what I'm trying to sort out in my head.

Thx,

TCS

Take ATO completely out of the loop...it doesn't mean anything to FAA rules and is only a reference to you. I don't understand your confusion. I don't have my 107. I can fly up to any man made structure at 400 feet AGL and can't go any higher period. So I could inspect (edit) shoot pictures of all parts of the man made structure for fun (in the correct airspace) from 400'AGL and down to the deck or zero AGL. This thread keeps spinning around this ATO term which only confuses others.

 

[Chaosrider]

Yeah crude and not quite to scale but I hope it's close enough to get the idea. Because water is a flat surface, once you hit the corner of the water and the terrain you'd have to begin to measure from there and stay 400' above the terrain directly below the drone. In the real world you should stay well below 400' in uneven terrain being you really have no way to accurately get a measurement.

There have been so many posts about staying 400' AGL I've been involved in, that the image posted has been my understanding when flying across a canyon (in this case a lake).

If I'm flying from the top of a hill and across a canyon, I have no reference to the actual distance to the ground, so I generally stay as close to the ground as possible (reasonable) while maintaining VLOS. It does force me to work closer to my home point, and be very aware of the drones surroundings.
Sheer cliffs are another issue. Although I'd like to be able to fly several few feet from the face of a 2000 foot vertical cliff and be in compliance, the rec rules (as I've seen it) say AGL is directly below the UAV. So depending on the slope, in many cases it makes a high sheer cliff flight almost impossible for me if I fly too far out away from the face. The steeper the cliff, the more difficult it is to know you're in compliance. I figure a 107 operation above/around a man made structure of 400' from it is simply because of the extra training involved that they are required to have. I'm actually surprised that there aren't restrictions on Rec flying too close to certain critical infrastructure especially towers and power lines.

View attachment 146473


I've never heard the term ATO (Auto Take Off came to mind) but figure it is the home point. Being the closest reference to altitude (what DJI telemetry offers) is from your home point, launching at the top of a hill then flying across a deep canyon might be confusing for some if they don't understand you gotta follow the terrain directly below the drone and never exceed 400' AGL.

I very much wish I could get a true AGL readout while I'm flying. But I can't.

In my case, the opposite wall of my canyon slopes pretty steeply, but it's not sheer. The creek at the bottom is 150 ft below my house. So what I'll frequently do is head toward the opposite wall at 250 ft ATO (which will keep me below 400 ft AGL at all times), and not start to climb until I cross the creek, and the canyon wall starts to slope up.

The reason I coined the ATO terminology for Above Take-Off, is because that's all you get to see on your screen. I've flown enough in this area now that I have a pretty good sense about what AGL at different altitudes looks like on the screen.

Keeping the relationship clear between ATO....which is what I can see on the screen...and AGL...which is what matters...helps to keep me within the 400 ft AGL rule.

I clearly had an initial misremembrance of the Rec rules. When I first started droning in May 2021, I didn't even know there were any rules, and as soon I discovered there were, I went and got my fixed wing BFR, and my drone 107. I never paid much attention to the Rec rules, but my early flights were so timid that I never came close to the edges.

Now, not so much...



Thx,

MM

 

[dronerdave]

I very much wish I could get a true AGL readout while I'm flying. But I can't.

I totally agree. I often fly in rolling hills around a lake. I launch at the lake and my controller records my ground launch site as zero. The lake is 20 feet below my take off point so if I fly down to the lake and drop down to 5 feet above the water, my screen shows minus 15 feet. If I fly to 20 feet above the water it shows 0 feet. If I fly 40 feet above the water it will show 20 feet.

So I like to do a video where I run towards a hill that slopes up to a high point, then drops back off again. What I do is to fly to the top of the bald hill (it's void of anything sticking up) and drop down as close as I can to the peak before reaching the ground. If that number (obviously I don't know the true height of the hill) is for instance 65 feet, I can use that as a reference point. I like to keep a safety buffer so I'll keep that in mind. I can go back away from the hill and adjust my drone to show 75 feet. I then turn on the camera, set my drone to sport mode and fly as fast as I can toward the top of the hill. I will be making a high speed run about 10 feet over the top of the hill. It makes for some cool video.

 

[66427cobra]

I very much wish I could get a true AGL readout while I'm flying. But I can't.

In my case, the opposite wall of my canyon slopes pretty steeply, but it's not sheer. The creek at the bottom is 150 ft below my house. So what I'll frequently do is head toward the opposite wall at 250 ft ATO (which will keep me below 400 ft AGL at all times), and not start to climb until I cross the creek, and the canyon wall starts to slope up.

The reason I coined the ATO terminology for Above Take-Off, is because that's all you get to see on your screen. I've flown enough in this area now that I have a pretty good sense about what AGL at different altitudes looks like on the screen.

Keeping the relationship clear between ATO....which is what I can see on the screen...and AGL...which is what matters...helps to keep me within the 400 ft AGL rule.

I clearly had an initial misremembrance of the Rec rules. When I first started droning in May 2021, I didn't even know there were any rules, and as soon I discovered there were, I went and got my fixed wing BFR, and my drone 107. I never paid much attention to the Rec rules, but my early flights were so timid that I never came close to the edges.

Now, not so much...

View attachment 146516

Thx,

MM

@Chaosrider

If, as you state, you are flying the same area, why not get a topographical map of that region which would show MSL altitudes? You could add/subtract the MSL on the topo map to/from the altitude your drone displays.

For example: If the topo map shows you are taking off from 600 ft. MSL (0 ft. on your drone display) and you then fly to an area on the map that is 100 ft. MSL the altitude on your drone would need to be between -500 ft. and -100 ft. to be legal (within 400 ft. AGL of that point).

You won't have true AGL displayed on your screen but you would have an approximate range within which to stay.

 

[Chaosrider]

Aviation regulations are made for aircraft that move far and fast, and for which takeoff altitude thus means nothing at all, AGL altitude will be different within seconds.
Note that most full scale pilots also have no measurement of AGL altitude and have to estimate just like you do, which is probably more difficult than the majority of drone flights where when you're within 500ish m of your takeoff point unless you're at the edge of a cliff ground level isn't going to change much.

I got my "full scale" pilot license 40 years ago, and I have over 1100 hrs of flight time.

For the vast majority of the time, you are correct, I had no AGL readout in the plane. But in 2012 I bought a shiny new Cessna C-162, and the Garmin 300 that it had did indeed provide an AGL readout, by integrating the GPS position with some terrain database.

I vastly preferred having that in-cabin AGL read out, to not having it.

I live and fly in a canyon. My house is built into the rock on one side of the canyon.

If I move more than 10 feet in any direction from my rear flight, ATO and AGL very quickly diverge.

On the forward flight deck, there is one, and only one, direction where ATO and AGL remain synced, and that's flying 100 ft straight down my driveway. Any other direction, and ATO and AGL immediately diverge.

Mountain flying was always very different from flatland flying in "full scale" aircraft, and it is with drones as well.

I've always preferred mountain flying to flatland flying.



MM

 

[Deleted member 93449]

I got my "full scale" pilot license 40 years ago, and I have over 1100 hrs of flight time.

For the vast majority of the time, you are correct, I had no AGL readout in the plane. But in 2012 I bought a shiny new Cessna C-162, and the Garmin 300 that it had did indeed provide an AGL readout, by integrating the GPS position with some terrain database.

I vastly preferred having that in-cabin AGL read out, to not having it.

I live and fly in a canyon. My house is built into the rock on one side of the canyon.

If I move more than 10 feet in any direction from my rear flight, ATO and AGL very quickly diverge.

On the forward flight deck, there is one, and only one, direction where ATO and AGL remain synced, and that's flying 100 ft straight down my driveway. Any other direction, and ATO and AGL immediately diverge.

Mountain flying was always very different from flatland flying in "full scale" aircraft, and it is with drones as well.

I've always preferred mountain flying to flatland flying.

View attachment 146522

MM

Absent technology on the drone that very accurately measures height above the ground the only way you can hope to stay compliant is using a significant margin of error when you fly. If you're flying in hilly terrain making judgements about AGL probably become more difficult as distances horizontally increase. Is the technology currently available conducive to putting it on small drones given considerations of cost, size and weight? Are they accurate enough to account for flying over trees, buildings or other object that could interfere with accurate readings of AGL and insure you don't bust the 400' limit?

 

[Chaosrider]

@Chaosrider

If, as you state, you are flying the same area, why not get a topographical map of that region which would show MSL altitudes? You could add/subtract the MSL on the topo map to/from the altitude your drone displays.

For example: If the topo map shows you are taking off from 600 ft. MSL (0 ft. on your drone display) and you then fly to an area on the map that is 100 ft. MSL the altitude on your drone would need to be between -500 ft. and -100 ft. to be legal (within 400 ft. AGL of that point).

You won't have true AGL displayed on your screen but you would have an approximate range within which to stay.

I just use the sectional chart. Works good!

I haven't flown a fixed wing airplane since last year, but my sectional subscription is current.



TCS