Question about the 400 ft. rule

[sar104]

I can see why there are sooo many restrictions in the US. If you can’t comply with the regulations, they will simply bring in more and more restrictions to cover the lowest common denominator who does the wrong thing.
simply 120m (400') agl is the limit not something suggested as a max height

Not (currently) for recreational flight. It has no set altitude limit in the US.

 

[Aussie Oldtimer]

so why is there a discussion about 400' LIMIT? if there is no limit?

 

[sar104]

so why is there a discussion about 400' LIMIT? if there is no limit?

Because people are confused. The default DJI firmware limit is 120 m (400 ft) above the takeoff location, though it can be raised to 500 m (1640 ft). Part 107 specifies a 400 ft AGL limit. Part 101 requires following the AMA guidelines, which don't specify a limit at all except in the vicinity of airports.

 

[Aussie Oldtimer]

Thanks

In Australia the limit is 120m (400’) and that’s it no more, full stop.
I have no idea what part 107 is but if one regulation restricts you to 400’ and another has no limit, that’s really confusing.

Does one part overrule another?

 

[sar104]

Thanks

In Australia the limit is 120m (400’) and that’s it no more, full stop.
I have no idea what part 107 is but if one regulation restricts you to 400’ and another has no limit, that’s really confusing.

Does one part overrule another?

Sorry - I should have clarified. 14 CFR Part 107 governs non-recreational flight and is the overarching regulation on sUAS operation in the US. 14 CFR Part 101 subpart E provides an exemption from Part 107 for recreational flight as was (foolishly) required by Congress in 2012, with fewer regulations.

 

[Flynz]

I think the RTH is a minimum level. If the drone is higher when you initiate I thought it holds that altitude. Even if above the set RTH. So over a mountain you would break the law as the drone flies over descending ground. I fly home manually. Easy enough to guess the altitude as land falls away.

 

[Flynz]

Thanks

In Australia the limit is 120m (400’) and that’s it no more, full stop.
I have no idea what part 107 is but if one regulation restricts you to 400’ and another has no limit, that’s really confusing.

Does one part overrule another?

In NZ we have part 101 amateur and part 102 licensed. Part 101 is 120m part 102 can fly higher with a flight plan and sometimes a radio. Similarly part 101 never able to fly in and ATC zone and part 102 can with a radio and tower clearance.

To confuse things Part 101 can fly in a zone with a qualified aircraft pilot supervising and in contact with the tower.

Restrictions also apply to within 4km of any airport. So all of Central Auckland is out due to three helipads . But you can fly sheltered which means no higher than the closest object within100m. That opens up quite a lot. Same is Ausy I suspect.

 

[Copter808]

I believe 400" Above the Ground means exactly 400" Above the Ground wherever you are, even if you are on Mt. Everest.

Correct.

 

[Simmo]

Nup we dont have the 'sheltered' rule. If its a NFZ then thats it. The exception is with a 'micro drone' ie under 100gms.

 

[Aussie Oldtimer]

To my mind, the 400’ rule is to prevent contact with other low flying aircraft. Most a/c don’t fly along valleys – except for the Mach Loop in Wales!

mach loop wales - Bing video

 

[John Locke]

Once you get above the tree tops the gusts are often stronger, but that's true at any altitude. I'm not sure that the tree line makes much difference for a drone flying well above ground level.

Correct, altitude and treeline has nothing to do with high wind frequency. The weather (barometer stability) is what determines the wind at any altitude. And like any place on earth, at any altitude, the weather can be hit or miss.

The Mt Lincoln video below was taken with flight altitudes up to ~14,300' MSL in Oct 2017. I launched from about 11,000' MSL. The craft flew fine, no abnormal behavior, but the wind was calm that week in the Rockies. The year before in Oct 2016 I wasn't so lucky, the wind was always about 25mph at all the passes. Hit or miss, same week of the year.

To answer the OP's question about RTH from high altitudes, if you follow the terrain of a mountain up to say 1500' (that's 1500' above launch point), but are sure that you are within 400' AGL, you are legal if you can see the craft from home point. In most cases you can't see the craft if you're 1500' up a mountain. Everyone fudges on that FAA rule, flying FPV BVLOS, but in reality this is fairly safe IMO, as manned fixed wing aircraft won't be in that area, unless a helicopter comes into the area, which you have to listen for. You do have to consider the likelihood of other craft like ultra-lights, para-sailors, etc. However, if your craft goes into RTH for battery or disconnect reasons, it will return to you at the altitude you lost signal, at 1500' above home point. If you can't retake control to keep the craft within 400' AGL, you're taking a huge risk, because that's not following a key FAA safety guideline of 400' AGL max. The craft DOES NOT descend to your programmed RTH height before heading home, as previously suggested.

Today there is no way to know exactly what your AGL is when flying mountains like that. You have to trust YOUR experience at flying and judging the AGL based on your view in your device screen. Good judgement for AGL altitude takes some time to acquire using the screen view. When I first started flying DJI drones FPV 3yrs ago I would challenge myself to guess the AGL number based on my screen view, then look at the telemetry to see how close my guess was. After a while I could do a fairly good job at judging my AGL height within 100' when flying below 400' AGL. I typically fly at around 150 to 200' AGL, but in mountains more like 300'.....most the time.

Also, I deem the 400' rule to be within 400' of land, in any direction, just like a "structure". Logically that's a safe flying rule, even though I haven't seen clarity in writing from the FAA. However when I ask this question of the FAA at NAB a couple years ago, they said 400' in any direction of land is acceptable for AGL. This means when flying off a 2000' cliff, as was the case in the Supersition Mtn video below, it's OK if you descend within 400' horizontally of the mountain wall.

Someday ....DJI will include actual AGL vertical estimates, without range finding hardware. This is doable with cell Internet service and some software. By accessing Google's MSL database using LAT/LON coordinates, the app could be designed to calculate an craft's AGL for any location the craft flies, near real time (maybe one calculation every 5 seconds or so). The vertical AGL altitude could be calculated to about 75' accuracy (IMO), using: 1. The home point MSL from Google's database (using the GPS LAT/LON at take-off), 2. The craft's altitude from home point (generally accurate to about 50') using the craft barometer. 3. The craft's current LAT/LON position AND Google's ground MSL for that coordinate. I'm actually surprised DJI hasn't offered this yet. I seems so simple, compared to other things they're doing. Although it's not super accurate, it would be more accurate than a pilot trying to judge AGL from the display view.

 

[Heyrob]

I'm wondering if following the terrain at less than 400 feet is in compliance with the letter & spirit of the 400 ft. AGL rule for drones. If I choose to fly up a mountainside, say to a 2,500 foot summit at 300 ft. AGL, am I an outlaw? Also, in this discussion, if my Return To Home altitude is set for 30 meters Above Ground Level, will the drone hug the mountainside at 30 meters AGL returning to me? Or, will it suppose I meant 30 meters above it's launch altitude? Any support for your opinions would be appreciated.

400' AGL is just that, 400' above the ground below the aircraft. The only exceptions are you must be a minimum of 500' below, and 2,000' horizontally from any cloud, and you can fly up to 400' above the highest point above a structure (Building, tower, etc.) as long as you're within a 400' radius around said structure, and the 400' above the structure does not extend into restricted airspace, without ATC permission.

I hope that helps understanding the 400' rule.

 

[sar104]

400' AGL is just that, 400' above the ground below the aircraft. The only exceptions are you must be a minimum of 500' below, and 2,000' horizontally from any cloud, and you can fly up to 400' above the highest point above a structure (Building, tower, etc.) as long as you're within a 400' radius around said structure, and the 400' above the structure does not extend into restricted airspace, without ATC permission.

I hope that helps understanding the 400' rule.

But to clarify - that's the requirement in the US for non-recreational flight under Part 107. None of those requirements applies to recreational flight under Part 101.

 

[FoxhallGH]

Bear in mind what the rule is there for and it may make it a bit easier to understand ... the 400 ft. [120m] AGL rule is there because (& yes - I'm simplifying this immensely!) general aviation [light aircraft etc.] fly under rules that state they should not fly lower than 500 ft nor closer than 500 ft to vertical structures (including towers etc.).
The idea being that if a drone and a light aircraft do get to share the same space, they should have at least 100 ft separation both horizontally and vertically.
That applies and shouldn't make a difference if you are at the beach, or half way up Mt. Everest!

[Edit: Them's the CAA rules in the UK anyway]

 

[TR Ganey]

I have a dumb question. What keeps a "107" pilot from flying under "101" rules when they are not on flights that require "107" certification?

 

[sar104]

I have a dumb question. What keeps a "107" pilot from flying under "101" rules when they are not on flights that require "107" certification?

Nothing. If the flight is recreational then that's perfectly legitimate.

 

[FoxhallGH]

I have a dumb question. What keeps a "107" pilot from flying under "101" rules when they are not on flights that require "107" certification?

It then starts to be more about 'intent' ... If you intend the flight to be for commercial reasons/gain - then it can't be 101 ...

 

[robstrong]

US regulations allow flight 400 feet AGL, or 400 feet above the top of an obstruction (tower, building), as long as the UAV is within a 400 foot horizontal radius of the obstruction. Cliffs are nothing if not an obstruction made of rock.

So if I were to fly over a 1,500 foot high cliff edge, I'd have to start descending within 400 horizontal feet.

Or: imagine the 400 foot regulation more like a thick blanket that wraps over and around obstructions and the earth itself, instead of merely [ground level + 400' at that precise lat/lon].

Or: Imagine a 400' bubble with your drone at the center. As long as some part of the bubble is touching something solidly attached to the planet, you're within the guidelines.

 

[sar104]

US regulations allow flight 400 feet AGL, or 400 feet above the top of an obstruction (tower, building), as long as the UAV is within a 400 foot horizontal radius of the obstruction. Cliffs are nothing if not an obstruction made of rock.

So if I were to fly over a 1,500 foot high cliff edge, I'd have to start descending within 400 horizontal feet.

Or: imagine the 400 foot regulation more like a thick blanket that wraps over and around obstructions and the earth itself, instead of merely [ground level + 400' at that precise lat/lon].

Or: Imagine a 400' bubble with your drone at the center. As long as some part of the bubble is touching something solidly attached to the planet, you're within the guidelines.

That's the rule for Part 107 flights. Recreational flights don't currently have an altitude limit.

 

[John Locke]

400' AGL is just that, 400' above the ground below the aircraft. The only exceptions are you must be a minimum of 500' below, and 2,000' horizontally from any cloud, and you can fly up to 400' above the highest point above a structure (Building, tower, etc.) as long as you're within a 400' radius around said structure, and the 400' above the structure does not extend into restricted airspace, without ATC permission.

I hope that helps understanding the 400' rule.

I always chuckle about the 500' rule below clouds. How do you measure that? A weather forecast?