400 ft. Flight Restriction - Mountain Flight - How to Comply

[sgreenwalt]

P3 flight / FAA compliance question:

I drove 400 feet up the side of a steep mountain on the Wasatch Front. Mountains run generally from South to North and I was on the West side.

I launched my drone and went to a height (from my position) of 200 ft.

Then I flew my drone to the West, away from the mountain . . . such that the ground dropped away from the drone due to the mountain slope.

Very quickly, the distance to ground increased to 600 ft. At this point, have I violated FAA rules?

The, I flew back toward the mountain, and then northward over ridges and valleys. During that time, the distance to ground varied with terrain changes (at times much below 400 feet, and at other times much above). There was no accurate way for me to assess the distance.

In general, gave I violated FAA rules?

If so, then how do I comply in such a situation?

If the above scenario does violate FAA guidelines, then aren't those guidelines just a bit like highway speed limits? I mean . . . who in their life has never exceeded the speed limit by at least 1 mph?

 

[kennedye]

Technically? Yes. However, you're pretty unlikely to encounter another aircraft flying within 40 feet of a mountain side, unless the pilot is a real Bud Holland type.

 

[John Locke]

You shouldn't fly at 400' AGL in the mountains imho. When I'm on a mountain I never go above 200' AGL, especially if I'm flying the crest of a hill. I usually try to stay below 150 or near tree tops. You have to use common since when flying a mountain crest, regardless who's right or wrong. This is because many small aircraft will fudge the guidelines for the same reasons, they know they are breaking the guidelines for about 5 seconds, while they get past the crest of the mountain. Sometimes it takes extra time and fuel to get up to 500AGL of a mountain crest in a small craft while at higher elevations. So they will barely clear the crest, often to get a close look of a mountain, but primarily to save fuel. Are they wrong?. Yes, but it don't matter. You must yield.

As for flying off cliffs, immediately descending to stay within the 400' guideline is my protocol. My rule is to stay within 200' of terra firma in all directions and I think I'll be safe from manned full size aircraft. Either 200' AGL vertically or 200' BMW (beside mountain wall) horizontally.

 

[sgreenwalt]

I just simplified the original question as follows:

P3 flight / FAA compliance question:

I drove 400 feet up the side of a steep mountain on the Wasatch Front. Mountains run generally from South to North and I was on the West side.

I launched my drone and went to a height (from my position) of 200 ft.

Then I flew my drone to the West, away from the mountain . . . such that the ground dropped away from the drone due to the mountain slope.

Very quickly, the distance to ground increased to 600 ft. At this point, have I violated FAA rules?

The, I flew back toward the mountain, and then northward over ridges and valleys. During that time, the distance to ground varied with terrain changes (at times much below 400 feet, and at other times much above). There was no accurate way for me to assess the distance.

In general, gave I violated FAA rules?

If so, then how do I comply in such a situation?

If the above scenario does violate FAA guidelines, then aren't those guidelines just a bit like highway speed limits? I mean . . . who in their life has never exceeded the speed limit by at least 1 mph?​

 

[RoyVa]

The answer is simple.... Don't exceed 400 ft. AGL as so the guidelines say.
Just think their guide line for small craft is don't drop below 500 ft. AGL that is suspose to give them a 100 clearance. Of course the only small craft this low would be the motorized para sailers, gliders, power kite, para motors,
Here is part 91'of the regs:
National Airspace System.
500 ft rule
An aircraft must maintain an altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure.
1000 ft rule
An aircraft must maintain an altitude of 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet of the aircraft over any congested area of a city, town, or settlement, or over any open air assembly of persons.

So we see why we have a 400 ft. Restriction

 

[tcope]

Very quickly, the distance to ground increased to 600 ft. At this point, have I violated FAA rules?

Were you more than 400' AGL? If so... yes.

During that time, the distance to ground varied with terrain changes (at times much below 400 feet, and at other times much above). There was no accurate way for me to assess the distance.

In general, gave I violated FAA rules?

Were you more than 400' AGL? If so... yes.

If so, then how do I comply in such a situation?

Stay below 400' AGL

If the above scenario does violate FAA guidelines, then aren't those guidelines just a bit like highway speed limits? I mean . . . who in their life has never exceeded the speed limit by at least 1 mph?

There are many people who fly more than 400' and many that don't. I think you already know the answers to all of your questions.

 

[Jeriami]

P3 flight / FAA compliance question:

I drove 400 feet up the side of a steep mountain on the Wasatch Front. Mountains run generally from South to North and I was on the West side.

I launched my drone and went to a height (from my position) of 200 ft.

Then I flew my drone to the West, away from the mountain . . . such that the ground dropped away from the drone due to the mountain slope.

Very quickly, the distance to ground increased to 600 ft. At this point, have I violated FAA rules?

The, I flew back toward the mountain, and then northward over ridges and valleys. During that time, the distance to ground varied with terrain changes (at times much below 400 feet, and at other times much above). There was no accurate way for me to assess the distance.

In general, gave I violated FAA rules?

If so, then how do I comply in such a situation?

If the above scenario does violate FAA guidelines, then aren't those guidelines just a bit like highway speed limits? I mean . . . who in their life has never exceeded the speed limit by at least 1 mph?

As the user above me noted, the FAA asks us to fly below 400', it was never a rule/law. For some reason a lot of people think they will be prosecuted if flying above 400', because it is a law. I think it is a good thing that people thing this is a law, because if everyone thought otherwise we would have everyone flying 1000' AGL. It is always better to stay below 400' as far as low flying aircraft go. In your situation, I would probably not even worry about going above 600' so close to a mountain.

 

[sgreenwalt]

It appears the 400 ft. ceiling is a safety guideline, and not a law, and not a rule. I reached that conclusion after reviewing all of the information the FAA has to offer on its web site, and the information offered at http://knowbeforeyoufly.org/for-recreational-users/.

My conclusion is that it is reasonable to expect flight above 400 ft. if the flight path crosses steep terrain that varies wildly in elevation.

Note that the DJI Pilot app calculates the height only relative to the launch point, and thus permits flight above the 400 ft. limit when the grounds drops out from under the P3.

 

[sgreenwalt]

P3 flight / FAA compliance question:

I drove 400 feet up the side of a steep mountain on the Wasatch Front. Mountains run generally from South to North and I was on the West side.

I launched my drone and went to a height (from my position) of 200 ft.

Then I flew my drone to the West, away from the mountain . . . such that the ground dropped away from the drone due to the mountain slope.

Very quickly, the distance to ground increased to 600 ft. At this point, have I violated FAA rules?

The, I flew back toward the mountain, and then northward over ridges and valleys. During that time, the distance to ground varied with terrain changes (at times much below 400 feet, and at other times much above). There was no accurate way for me to assess the distance.

In general, gave I violated FAA rules?

If so, then how do I comply in such a situation?

If the above scenario does violate FAA guidelines, then aren't those guidelines just a bit like highway speed limits? I mean . . . who in their life has never exceeded the speed limit by at least 1 mph?

It appears the 400 ft. ceiling is a safety guideline, and not a law, and not a rule. I reached that conclusion after reviewing all of the information the FAA has to offer on its web site, and the information offered at Recreational Users | Know Before You Fly.

My conclusion is that it is reasonable to expect flight above 400 ft. if the flight path crosses steep terrain that varies wildly in elevation.

Note that the DJI Pilot app calculates the height only relative to the launch point, and thus permits flight above the 400 ft. limit when the grounds drops out from under the P3.

 

[Meta4]

You were saying that "I am trying to say that flying near steep terrain (like a mountain) makes it impossible to comply with the FAA 400 ft. restriction because the distance to ground varies rapidly, AND the P3 does not report true distance to ground, AND because there is no way to visually gauge the distance to ground."

But this is not right. It's not impossibe at all.
What do you think Joe Pilot in his Cessna 185 does?
The VFR rules he has to comply with are:

14 CFR 91.119 Minimum safe altitudes: General.
Except when necessary for takeoff or landing, no person may operate an aircraft below the following altitudes:
...
(b) Over congested areas. Over any congested area of a city, town, or settlement, or over any open air assembly of persons, an altitude of 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet of the aircraft.
(c) Over other than congested areas. An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure. ​

But his Cessna has no way to tell how high above the terrain it is flying.
All Joe knows is how high above sea level he is.
The solution for JP is to use common sense do a little thinking to work it out.
And that's what Phantom flyers have to do as well.

 

[John Locke]

Then I flew my drone to the West, away from the mountain . . . such that the ground dropped away from the drone due to the mountain slope.
Very quickly, the distance to ground increased to 600 ft. At this point, have I violated FAA rules?​

Some common sense may be all that's needed. I my book I always stay within 300' of land (usually it's ~200'), vertical or horizontal when I'm in mountain/valley situations, that's my SOP. When I'm in the mountains I use the principle in the illustration below to stay less than 300' from land in any direction. I feel I'm being safe enough and abiding by FAA guidelines. Common sense says planes shouldn't be flying that close to the side of a mountain, so I'm not in danger unless I'm in an area where hang gliders or ultralights might fly (again, common sense).

Judging distance from the side of a mountain isn't difficult with practice. Using my view from the Ipad, I've flown within 10' of lighthouses over a mile away from my launch point, so staying within 300' is cake. If you're 800' AGL when flying off a mountain cliff, if you're within 300' of the side of the cliff you should be good, in my book. I cruise mountain crests like this all the time below the rim, but I'm still way higher than 400' straight down. I just hug the mountain within 200' of land, being the side of the mountain. It makes some great video if you're not in the shadow of the mountain.

When on top of mountain crests I reduce my flight height even less, down to about 100'. This is because private pilots will fudge the numbers and push the guidelines, clearing high mountain crests only by a hundred feet or so. This saves time and fuel, plus it's a rush to get close up views of the ground at times. In sparsely populated areas many pilots will fly low, so I try to be aware of that possibly and stay cautious in mountain peak areas, like when I few Loveland Pass last Sept at 12,000' ASL! The continental divide area in the Rockies is really fun to fly. The reveal as you look over the crest is really amazing.

Remember, the FAA numbers are guidelines and many situations may only need some common sense.

 

[mikeshin]

Follow up question - if I do always stay 400 AGL off of the mountain and the drone is now below my altitude, what happens when failsafe activates and it goes into RTH? I assume it'll attempt to run into the mountain at its current altitude (below me)? Anyone experienced this?

 

[Roamer105]

Follow up question - if I do always stay 400 AGL off of the mountain and the drone is now below my altitude, what happens when failsafe activates and it goes into RTH? I assume it'll attempt to run into the mountain at its current altitude (below me)? Anyone experienced this?

RTH altitude is relative to take-off altitude and not AGL. So, let's say your RTH altitude is set to 400 feet. If you fly off a ledge over a canyon and drop down 200 feet you are 200 feet below takeoff altitude. if you invoke RTH at that point, it will climb straight up 600 feet before moving back towards home point.

I agree with John regarding reasonable safety. Recently I flew a very deep canyon off the rim. Immediately, my P3P was several thousand feet AGL, yet I was only 100' away from a nearly vertical wall slightly below the rim. Not even a helicopter would fly that close.

 

[WetDog]

Follow up question - if I do always stay 400 AGL off of the mountain and the drone is now below my altitude, what happens when failsafe activates and it goes into RTH? I assume it'll attempt to run into the mountain at its current altitude (below me)? Anyone experienced this?

This is actually an excellent question and Roamer105's answer is right. But here you can get into a situation where you are above 400 feet AGL rather quickly. Lets say you drop off the mentioned canyon, staying close to the wall. You then fly over the valley several hundred feet lateral and still at 150 feet AGL (the valley floor). RTH kicks in, the craft will now rise to the takeoff height plus the RTH height. Now it can be way out in the middle of the valley, right in the space that a Cessna might fly.

So it pays to think about where you are going to fly and what can happen if things go wrong. In all likelihood, you are going to be exposed for a couple of minutes and if you are in the Utah desert or thereabouts, likely not going to be in the way of the Cessna. But I might hesitate to fly in an area where I knew that the UAV could end up where it didn't belong if things went wonky. That's one of the reasons for the wide restriction around airports. These things usually, but not always, behave correctly.