400' AGL

[John235]

Be careful setting your RTH height. If you should happen to lose connection while the drone is at the top, your RTH height would have to be above 400' or risk obstacle interference. Even if your RTH height were set to, say, 200 ft, and you lose signal when the drone is up the mountain at, say, 600 ft above home, yet only 100 ft AGL, a loss of signal would cause the drone to ascend to 200 ft AGL, OR 800 above home for the return. Be particularly careful flying any intelligent flights, such as waypoint missions that might put an obstacle between your drone and home.
Guys, is my math correct?

Edit: Just realized my error. No, it is not correct. The RTH height is measured above home point. So if the drone is 100 above ground while over ground that is 600 ft above home, it is actually flying at 700 ft above home. If the RTH height is 200 ft, the drone will not descend, but remain at 700 ft for the return. Not only would it be above 400 on the return, while out of your control, but there is a risk initially of not being high enough for intervening obstacles.

 

[The Fat Controller]

Not to nit pick, but all the "400 ft" arrows should be vertical.

The one in the middle had a few pints at lunch time ???

 

[sar104]

Be careful setting your RTH height. If you should happen to lose connection while the drone is at the top, your RTH height would have to be above 400' or risk obstacle interference. Even if your RTH height were set to, say, 200 ft, and you lose signal when the drone is up the mountain at, say, 600 ft above home, yet only 100 ft AGL, a loss of signal would cause the drone to ascend to 200 ft AGL, OR 800 above home for the return. Be particularly careful flying any intelligent flights, such as waypoint missions that might put an obstacle between your drone and home.
Guys, is my math correct?

RTH height is above the takeoff point, so if you set it to more than 400 ft or if it would pass over terrain significantly lower than the takeoff point then that could certainly cause the aircraft to exceed 400 ft AGL. But if you lost connection above the top of the hill, even if the RTH height were set to zero, then it would return to the home point at its current height and exceed 400 ft AGL.

 

[bobscheel53]

Not to nit pick, but all the "400 ft" arrows should be vertical.

Actually the drawing is correct. If it was a sheer cliff with a 700 ' drop you are still legal within 400 ft of the side.

 

[BigAl07]

Actually the drawing is correct. If it was a sheer cliff with a 700 ' drop you are still legal within 400 ft of the side.

Please cite your source for this broad allowance and be specific because there is a difference between Hobby and Part 107 and there's also a difference between a Hill and a Structure. . . .

 

[sar104]

Actually the drawing is correct. If it was a sheer cliff with a 700 ' drop you are still legal within 400 ft of the side.

No - the drawing is not correct under the current US regulations. The requirement is 400 ft AGL. The only allowance beyond that is for Part 107 flights in the vicinity of structures.

 

[Milo187]

Let's say he takes off from the top of the hill and heads to the right in this illustration. How does he determine his exact height while flying over the "valley"?

Never really put that to the test but I believe Go4 will display negative AGL if you’re below the registered launch point.
Anyone ever seen this? I seem to recall several flights I’ve had in the past like this but didn’t really pay attention.

 

[sar104]

Never really put that to the test but I believe Go4 will display negative AGL if you’re below the registered launch point.
Anyone ever seen this? I seem to recall several flights I’ve had in the past like this but didn’t really pay attention.

The telemetry doesn't display height AGL - it displays height relative to the takeoff point elevation. And yes - that will go negative if you fly below that elevation.

 

[Milo187]

Never really put that to the test but I believe Go4 will display negative AGL if you’re below the registered launch point.
Anyone ever seen this? I seem to recall several flights I’ve had in the past like this but didn’t really pay attention.

Looking at the PhantomPilots posts on this it is correct that it will display negative altitude based on the launch point so you just need to be aware of the terrain heights and calculate accordingly.

 

[Mavic3]

The term AGL, or above ground level, is interchangeable with absolute altitude, as they measure the same distance. It is the measured altitude of an aircraft above the underlying ground that it is flying over

 

[ToddCarey]

Anytime you are at the base of a hill and flying up the hill, but very careful not to go past the top. Not only will you lose the VLOS, but the digital signal of these units does not give a lot of warning before it is gone.

 

[Starz]

Never really put that to the test but I believe Go4 will display negative AGL if you’re below the registered launch point.
Anyone ever seen this? I seem to recall several flights I’ve had in the past like this but didn’t really pay attention.

Yes, it does display negative numbers when you fly below launch point.

 

[Montana John]

View attachment 77383

Shouldn't all three 400 ft. lines be vertical, parallel to each other?

 

[InvisibleName]

Gotta say this is a really entertaining thread to follow! So many opinions! ?

 

[Thomas B]

Let's say he takes off from the top of the hill and heads to the right in this illustration. How does he determine his exact height while flying over the "valley"?

I take it that you mean altitude from the ground below the drone. VFR or knowing the relative elevations and doing the math is the answer. All will be relative to TO point (Home Point) positive or negative.

 

[Sprocket]

I take it that you mean altitude from the ground below the drone. VFR or knowing the relative elevations and doing the math is the answer. All will be relative to TO point (Home Point) positive or negative.

Look at the illustration on page one. Tell me what the is the different elevations between the top of the hill and the waters edge.
Let's say it is a really steep hill and the water is 1000' away. How do I know if I am 400' when I get to the water? The drone is reporting negative numbers in relation to my takeoff elevation, but I have no idea how far it is down to the water level.

 

[Thomas B]

Look at the illustration on page one. Tell me what the is the different elevations between the top of the hill and the waters edge.
Let's say it is a really steep hill and the water is 1000' away. How do I know if I am 400' when I get to the water? The drone is reporting negative numbers in relation to my takeoff elevation, but I have no idea how far it is down to the water level.

You have to know the relative elevations from a map.. piloting skill.
I have the same concern you express when I launch from the top of the Mogollon Rim.., it’s a 2000’ high 300 mile long cliff crossing north central AZ. When I take off the home point is on top and my relative (to home point) and absolute altitude is 4 ft. When I fly 25 feet south my absolute altitude is about 2004’ as I fly out beyond the edge of the Rim.
You can use the negative number registered by your drone when you fly to a point below home point along with either flight or topo maps to compute altitude from the ground below.

 

[Sprocket]

You have to know the relative elevations from a map.. piloting skill.
I have the same concern you express when I launch from the top of the Mogollon Rim.., it’s a 2000’ high 300 mile long cliff crossing north central AZ. When I take off the home point is on top and my relative (to home point) and absolute altitude is 4 ft. When I fly 25 feet south my absolute altitude is about 2004’ as I fly out beyond the edge of the Rim.
You can use the negative number registered by your drone when you fly to a point below home point along with either flight or topo maps to compute altitude from the ground below.

Look at a lot of videos of mountain flying. They are flying illegally, legally, unknown and just about everything else all at the same time. Sure makes for beautiful photos though.
Anytime someone takes off from the top of a hill and immediately ascends to 400' will supposedly have to start descending as soon as they encounter the start of the slope. Like anyone ever does.

 

[Starz]

Look at the illustration on page one. Tell me what the is the different elevations between the top of the hill and the waters edge.
Let's say it is a really steep hill and the water is 1000' away. How do I know if I am 400' when I get to the water? The drone is reporting negative numbers in relation to my takeoff elevation, but I have no idea how far it is down to the water level.

From the illustration on page one.
From the top of the hill, at about negative 265, you’re probably going swimming.
(WAG. terminology I remember from some estimating class years ago)
wild a_ _ guess

 

[sar104]

Gotta say this is a really entertaining thread to follow! So many opinions! ?

The opinions may be entertaining, but it's the facts that are actually useful.