I'm not here to argue FAA rules, simply P4 capabilities and techniques flying in a mountainous environment.
I flew my P4 in the mountains recently.  Started out with max altitude at 120 meters (400 feet) per FAA regulations.  As I flew up the mountainside the familiar voice told me I had reached max altitude.  This kept me from flying further "up hill".  It appears the P4 simply uses the altitude at the take off position versus the current (flying) AGL altitude.  For those not familiar with AGL it is the "Above Ground Level" altitude used by aircraft.  It simply means the actual altitude above the ground directly under the aircraft (quad, bird, etc.) I would have hoped the P4 would know the current land elevation under the P4 and adjust the max altitude to the current AGL vs. from the take off position.  This forces the pilot to increase the max altitude to the level necessary to fly "up hill".  I have read input suggesting updating the home point to the current position once you have flown to max altitude thus allowing you to climb higher and go further "up hill".  My concern is the effects of doing so and losing connectivity with the controller and having the P4 land in the woods during RTH.  That said, against my better judgement I increased the max altitude to 500m and successfully flew the P4 to an altitude great enough to fly "up hill" and was never above 120m AGL but was 500m above my takeoff position.  What if I wanted to fly higher?  How could the P4 do so?  Lastly, to keep the FAA rat squad from getting worked up, my intention is not to fly it above 120m AGL which I believe is well within the FAA regulations.  Seeking input from pilots smarter than me.  What say you?  Bonus points for actual experience vs. speculation.  Thanks in advance!

All the Phantoms use a barometric pressure device to read altitude, this is calibrated to zero each time you switch on the Phantom.
So the take-off point is always zero no matter what the AGL height is.
That's why if you take off from the top of a hill and fly down you will see a negative altitude reading.

So if you want to fly higher, you need to climb further up the hill before you take-off.

Good input.  thanks.  If I set the max altitude to 500m what would be the max RTH altitude allowed by the P4?

RTH altitude is set from the take-off point, which is zero + whatever you have set the RTH altitude to in the app.
However if the Phantom is higher than the RTH set altitude when it goes into RTH it will stay at that height, it will not descend to the set RTH altitude.
I don't know what the maximum RTH altitude is, never need to change mine from the default, but I guess it will not allow you to set more than the 500m limit.
Hope I am making sense, forgot how complicated these things can get....

Makes sense.  In the scenario I described I would only fly from a lower takeoff position and fly up hill not going over or around any peaks.  This way I have a better chance of maintaining controller contact and avoiding any RTH mishaps.  During the flight described I was able to investigate an empty osprey nest.  It was pretty cool but forgot to video the event due to max pucker factor.  It will surely be there next time I'm at the location.  Even though I have a Marco Polo RF tracker attached to my P4 it was still hair raising flying over a river and up a mountainside.  Recovery would have been a real chore should I have suffered a mishap.

Yeah if you fly behind the peaks you have a good chance of losing control signal and the Phantom trying to RTH through the mountain, not a pleasant thought...
I wish you good luck with your plan

Luckily my 'mountain' is only 425m elevation.

Buy Low Posted at 2016-6-8 11:24
Makes sense.  In the scenario I described I would only fly from a lower takeoff position and fly up  ...

Aloha Buy Low & john,

     What you are proposing and apparently have done is well within regulations and guidelines, so be sure you are backing up your flight records and sync your flights like this to the DJI server.  That way, if there are any questions about this valuable effort, you have the evidence of your flight records.  It is easy to establish that you were consistently below 400 feet with your method.  (The DJI limitations just make it easier for you to stay below the 400 foot limit.)

     You may or may not have seen the Mountain Math video on how to use Kneepuck's system to go higher than the DJI voluntary (software) limitations.  Two options are shown.  In the video, 100 feet is gained by landing, stopping and restarting the motors at an alternative home point and then adding 400 feet (for the 120 meter limit).  The second 400 feet is done with a hand catch and stopping and restarting the motors at the higher new home point.  

     In your case, you could have a spotter stationed 500 meters, or close, up the side of the mountain (instead of my 120 meters).  If there is a safe landing spot, like a dome, then use it, otherwise have your spotter do a hand catch and release for 500 more meters.  The P4 is amazing when landing in precise locations.   Three feet by three feet is plenty of space.  But, be aware that the lip of the location can block the RC signal when you are 1000 feet below.  It might be a good idea to experiment with your spotter at the higher, alternative, home point.  That way, if the lip blocks the signal, they can do a hand launch.

     Go for it!  Sounds like fun!

Aloha and Drone On!

RTH I think is set to 100' from take-off and this can be changed due to changing envroments (changing because you change spots).

I fly in the mountains exclusively.  You should not have any problems.  The max altitude you can achieve is 1640 feet above takeoff point.  But so long as you are max 400 feet agl,  no worries.  As far as rth goes,  the Phantom will ascend to preset rth height only if it is below that height.  If it is above that height,  it will beeline home and descend once over the home point,  unless rth is initiated within 20 meters of home point,  at which time it will just come straight down.

Have fun.

Great info Kneepuck & Cetaman.  I cannot use the land and takeoff or buddy up the hill strategy due to the terrain.  Very steep and heavily wooded.  However, setting the max altitude to 500m and maintaining an AGL altitude of <120m will get the job done for me.  Thanks again for the advice.

The app I use for mountainous flight, and others, is DJI Ultimate Flight (UF) which will use AGL derived from Google Earth elevation models or from your own DTM's. So, I have my max altitude set at 500m and set up my flight plan along the hillside making sure to have waypoints at significant elevation change points and UF autonomously flies the drone maintaining the AGL. It's pretty slick.

You use DJI Ultimate Flight with the Phantom 4?

I've just searched on the App Store and can't find it.  Is it an official DJI app?

Never mind I googled and see it is only for Android, and Litchi looks better in any case

treeboyy Posted at 2016-6-10 08:40
The app I use for mountainous flight, and others, is DJI Ultimate Flight (UF) which will use AGL der ...

What happens if you set a waypoint above 500 meters? Does the drone fly to the waypoint altitude or crash into the ground at 500 meters if it is higher than that relative to the start point?

treeboyy Posted at 2016-6-10 08:40
The app I use for mountainous flight, and others, is DJI Ultimate Flight (UF) which will use AGL der ...

sounds like a good option for mountainous flight.  I'll have to wait for it to come out for Apple devices as I've gone to the dark side.  Thanks for the input.

malvern Posted at 2016-6-9 07:19
Luckily my 'mountain' is only 425m elevation.

https://www.youtube.com/watch?v=5L8KObUGUkk

Absolutely gorgeous! Just got my P4 yesterday and am new to drones, so maybe I am more easily impressed than the old salts, but it is for videos like this one that I am inspired to try my hand at this craft. And I love your choice of music.  I'm curious, are the colors, contrast and brightness straight from the camera or did you apply some edits (I know I'm straying from the point of the post - sorry)?

rogerTHAT Posted at 2016-6-13 02:27
Absolutely gorgeous! Just got my P4 yesterday and am new to drones, so maybe I am more easily impr ...

Thank you, it's all unedited and straight off the SD card.

FPV Camera app is for iOS with Terrain Elevation feature built-in the app http://fpvbooster.com/index.php? ... w=article&id=66

grangerfx@gmail Posted at 2016-6-13 00:21
What happens if you set a waypoint above 500 meters? Does the drone fly to the waypoint altitude o ...

Well, you can't set the altitude above 500 meters, that's all firmware accessed by the software (DJI Go) settings. However, if one sets waypoints on either side of a ridge then perhaps the drone will crash (P3) because the AGL is taken at the waypoint only not all along the track.

treeboyy Posted at 2016-6-16 17:36
Well, you can't set the altitude above 500 meters, that's all firmware accessed by the software (D ...

Aloha treeboy,

     Sorry, but that is not a "perhaps".  It is a firm and often repeated, "Yes it will crash into the mountain, house, building, tree, etc." if you set waypoints on opposite sides of an obstacle.  No worries though, we know what you meant.  I am only saying this because some newbies may not catch what you are saying.

Aloha and Drone On!

Cetaman Posted at 2016-6-17 00:07
Aloha treeboy,

     Sorry, but that is not a "perhaps".  It is a firm and often repeated, "Yes it ...

I hear you, I was just suggesting that "perhaps" a P4 my employ the object avoidance and not crash. Thankfully I haven't found out yet.

treeboyy Posted at 2016-6-17 12:50
I hear you, I was just suggesting that "perhaps" a P4 my employ the object avoidance and not crash ...

Aloha treeboy,

     Really!  I could not agree with you more.  However, I do not want to be the one to find out.  I like taking the scenic route around the obstacle.

Aloha and Drone On!