The altitude problem.

[Andy9]

I'm sure that this was discussed already but I just couldn't find it.
Taking off from the hill and ascending to let say 100m. Then you fly at straight line forward away from the hill keeping the same altitude.
But the slope of the hill quickly causes the altitude to become a few 100 m from the ground, although you have still 100m on the display.
How can one keep the drone below those 120m (400ft) if the distance to the ground is not known in such circumstances?

 

[Fly Dawg]

How can one keep the drone below those 120m (400ft) if the distance to the ground is not known in such circumstances?

400 ft is based on the takeoff location. If you takeoff on a 100 ft hill and fly up another 300 ft, you are at the 400ft level. It makes no difference if the aircraft is past the hill and 500 ft from the actual ground below the hill. You are still within your 400ft max based on the takeoff point.

 

[Fly Dawg]

EDIT TO ABOVE: The aircraft only knows it's zero reference, which is set at the takeoff point. As long as you remain below 400ft AGL at any point up hill, down hill does not matter. Manually this is a bit tough to discern actually. Flying autonomously can be easily compensated. I misstated this previously.

 

[2edgesword]

As Fly Dawg stated in his 2nd post the issue is going to be where you are above ground level at the moment, meaning the ground below the drone at any given point in time.

That said I'm wondering if there is some lateral consideration on this as there is for flying near a building or other structure. You can fly 400' above the building even if the height of the building or structure is greater than 400' as long as you are with 400' horizontally of the building. I don't see any place where this same logic is applied to terrain and even if it did it would be hard to keep track of it on a hill where terrain isn't following a regular incline/decline.

 

[3rdof5]

As Fly Dawg stated in his 2nd post the issue is going to be where you are above ground level at the moment, meaning the ground below the drone at any given point in time.

That said I'm wondering if there is some lateral consideration on this as there is for flying near a building or other structure. You can fly 400' above the building even if the height of the building or structure is greater than 400' as long as you are with 400' horizontally of the building. I don't see any place where this same logic is applied to terrain and even if it did it would be hard to keep track of it on a hill where terrain isn't following a regular incline/decline.

Well said!
To be safe I'd follow the "over the building rule". If you want to take off at the top of a cliff 400m high and think ur safe to just go out laterally, I'd disagree. Stay within the max height of the terrain below you regardless of takeoff altitude.

 

[Meta4]

Taking off from the hill and ascending to let say 100m. Then you fly at straight line forward away from the hill keeping the same altitude.
But the slope of the hill quickly causes the altitude to become a few 100 m from the ground, although you have still 100m on the display.
How can one keep the drone below those 120m (400ft) if the distance to the ground is not known in such circumstances?

You would have to estimate just like general aviation pilots do.

 

[Andy9]

As far as I understand this situation you are not within 400ft if you launch from top of the hill and you stay within your 100m above launch point while you fly over the valley which is 1000m below. You are then actually 1100m from the ground as nobody will know from where you took off and the same is with the pilot of the aircraft which may fly along this valley.

 

[mrozburn]

We have the same type of issue, only in reverse. Our agency flies logging operations to do inspections on roads, streams, etc, and in some parts of the state, the only good launch location is in the hollow, but the job covers the hillside, which can often rise over 400’ in elevation from the home point. We currently consider it ok if we allow for max 400’ over the terrain, or no more than about 200’ over the treetops. Having said that, it’s still an issue we struggle with and don’t like having to up the max altitude level in the GO4 app.

 

[Jiminy Cricket]

400' AGL or stationary structure. That's the rule in USA. The drone can not exceed 400' AGL. The 400' will move as the terrain/building ascends or descends. Doesn't matter where you take off from.

 

[solentlife]

I think its a case of some desk jockey has worded the rule and assumes it will be obeyed. Taking no regard for those who will fly in irregular terrain. I suggest they wrote it thinking most fliers will be in parks or generally level areas ...

Its not only USA that has a max flying height for models ... but regardless of what the national figure is - if you are apprehended by authorities flying at greater than the limit based on where THEY observe - I think it will be a matter of discussion as to whether they accept your take-off point stance. Of course if you can show the height displayed on screen - you would possibly have a strong case in your favour.

Its a matter that has had a lot of debate and discussion not only on this forum, but others as well.

 

[sar104]

I think its a case of some desk jockey has worded the rule and assumes it will be obeyed. Taking no regard for those who will fly in irregular terrain. I suggest they wrote it thinking most fliers will be in parks or generally level areas ...

Its not only USA that has a max flying height for models ... but regardless of what the national figure is - if you are apprehended by authorities flying at greater than the limit based on where THEY observe - I think it will be a matter of discussion as to whether they accept your take-off point stance. Of course if you can show the height displayed on screen - you would possibly have a strong case in your favour.

Its a matter that has had a lot of debate and discussion not only on this forum, but others as well.

There doesn't have to be any ambiguity at all - you download the flight log and plot the flight on Google Earth, which will immediately show exactly the aircraft height AGL for the entire flight.

 

[Meta4]

Having said that, it’s still an issue we struggle with and don’t like having to up the max altitude level in the GO4 app.

Height above launch point is irrelevant.
The FAA understand that the earth is not pancake-flat.

I think its a case of some desk jockey has worded the rule and assumes it will be obeyed. Taking no regard for those who will fly in irregular terrain. I suggest they wrote it thinking most fliers will be in parks or generally level areas ...

Its not only USA that has a max flying height for models ... but regardless of what the national figure is - if you are apprehended by authorities flying at greater than the limit based on where THEY observe - I think it will be a matter of discussion as to whether they accept your take-off point stance. Of course if you can show the height displayed on screen - you would possibly have a strong case in your favour.

Its a matter that has had a lot of debate and discussion not only on this forum, but others as well.

No debate is necessary..
No authority in the world cares about your altitude relative to your launch point because it makes no sense at all.

What's a hypothetical FAA inspector going to do when he comes across this situation?
Two drones a few feet apart - obviously both are equally within altitude regulations.

 

[Andy9]

Thanks. I just want to be sure. It is logical. The explanation is correct and need no further argumentation.

Be aware of that if you want to take pictures of Grand canyon or some spectacular cliff.

 

[solentlife]

No authority in the world cares about your altitude relative to your launch point because it makes no sense at all.

What's a hypothetical FAA inspector going to do when he comes across this situation?

I disagree for simple reason .... That hypothetical Inspector if he is standing at point B in your diagram - unless you can prove from flight log etc. that you took of and were within the limit referenced to A location - he will reference you to HIS B location - putting you ABOVE the limit.

I would also suggest that given low flying aircraft and possible daredevil antics of flying BETWEEN high hills - WE are at a disadvantage.

My own PoV is that if I was to fly from crest of a hill with significant valley next to it .... I would stay close in to avoid any possibility of 'misunderstanding' .....

 

[THA]

Some of you guys are misusing the term AGL. AGL means above ground level. It varies depending on terrain. If you take off from point "A" and it is 100'MSL and ascend to 400' above that point you are at 400'AGL and 500' MSL. If you fly a certain distance horizontally and are above a higher point, say 300' MSL you are now at 100' AGL and can ascent 300' higher making you 700' MSL still legal. Conversely, if you take off at a point 1000' MSL and ascend to 400' AGL you are now at 1400'MSL. Now fly horizontally over a lower point that is 600' MSL you are now at 800'AGL but still 1400' MSL. Well above your 400' AGL limit. MSL is mean sea level and AGL is above ground level at the point where you actually are above the ground.

Flight log will only show delta altitude difference from takeoff point.

Consider you take off from a point 100'MSL and ascend to 500'MSL or 400'AGL and fly horizontally to another point which is also 100'MSL but in doing so you fly over a valley which is 25' MSL, you have violated the 400 AGL rule while flying over it by 75' You were at the original 500' MSL which was legal at takeoff and final point but in doing so while flying over the 25' MSL point, you were 475'AGL and in violation.

 

[N017RW]

I disagree for simple reason .... That hypothetical Inspector if he is standing at point B in your diagram - unless you can prove from flight log etc. that you took of and were within the limit referenced to A location - he will reference you to HIS B location - putting you ABOVE the limit.

I would also suggest that given low flying aircraft and possible daredevil antics of flying BETWEEN high hills - WE are at a disadvantage.

My own PoV is that if I was to fly from crest of a hill with significant valley next to it .... I would stay close in to avoid any possibility of 'misunderstanding' .....

An aircraft's height/altitude/distance AGL has nothing to do with where any inspector is standing.

It's the aircraft's height/altitude/distance AGL.

Thus the AGL is always measured directly below the aircraft.

 

[Meta4]

I disagree for simple reason .... That hypothetical Inspector if he is standing at point B in your diagram - unless you can prove from flight log etc. that you took of and were within the limit referenced to A location - he will reference you to HIS B location - putting you ABOVE the limit.

To follow that peculiar "logic", when the inspector gets out of his car at the carpark in the valley, everyone is going to get a ticket?

If one of those drones is legal, both are legal.
It's hard to see how there could be any confusion.
Fortunately aviation safety authorities understand what AGL means even if you don't.

 

[solentlife]

An aircraft's height/altitude/distance AGL has nothing to do with where any inspector is standing.

It's the aircraft's height/altitude/distance AGL.

Thus the AGL is always measured directly below the aircraft.

Totally agree with that .... what you and Meta4 miss in my PoV is that the AC when it flies over the head of that Inspector, in his interpretation of the rules AGL is based on where he is standing ... not the flyer with RC up the hillside.

Car Park !!!! That's funny !!

The fundamental problem here is the derivation of the height the AC is flying at. The display and flight log all list it as relative to take off point as Zero. As the AC moves out from the hillside over the valley - it is displaying the same referenced height. So saying take off point is irrelevant is 100% wrong. It is relevant to the person controlling the AC.
When it comes to another person IN THE VALLEY - if the AC hovers above his head regards the AC height as referenced to directly below that AC where he is.

As I see it and it has been a subject of debate in the Group I am in who report to EU / Latvian Aviation Authority - the problem is interpretation of what is the actual height reference ... So far on this and other forums I frequent and the Larpas group mentioned - a definitive statement is yet to be made. People SAY they have it ... but in fact they don't.
People love to quote Aircraft terms such as AGL ... MSL .... etc. but they cannot be determined by the flyer of his drone. All he has is Take Off point referenced height which is only AGL on his display when AC is directly over that point. Everywhere else its just BS.

 

[solentlife]

To follow that peculiar "logic", when the inspector gets out of his car at the carpark in the valley, everyone is going to get a ticket?

If one of those drones is legal, both are legal.
It's hard to see how there could be any confusion.
Fortunately aviation safety authorities understand what AGL means even if you don't.

You really have missed the boat .....

I completely understand AGL and many other aeronautical terms. What you are doing is using a singular aspect diagram for your point ignoring the fact that if the AC is directly overhead of the person to the right ... you have him in blue ... FOR HIM and in fact AGL is height at that point ..... not at flight origin.

I have never in any post stated the AC stayed up the hill over the take off area.

 

[Meta4]

You really have missed the boat .....

I completely understand AGL and many other aeronautical terms. What you are doing is using a singular aspect diagram for your point ignoring the fact that if the AC is directly overhead of the person to the right ... you have him in blue ... FOR HIM and in fact AGL is height at that point ..... not at flight origin.

I have never in any post stated the AC stayed up the hill over the take off area.

I've read that 3 times and still can't work out what you are saying.
Going back to what you wrote previously, doesn't make much sense either.
btw .. The man in blue is the hypothetical inspector.
For him or anyone else, AGL is height above the ground, and the ground being referred to is always the ground directly below the aircraft.
There's no other way to interpret it and my diagrams make that pretty clear to everyone else.