From time to time I check some of the safety features, like e.g. "Smart Return Home", just to see if and how they are functioning.
So today I flew outbound with 17% battery left only 100 m away at 38m altitude beyond the "H" (Home) symbol of the "battery life timeline" (into its yellow band area).
The "Smart Return Home" function initiated (with cancel slider screen) and I let it do its thing. I noticed that it turned and flew towards the home point,
but it stayed at 38m instead of climbing to 50m (set as the "Return Home Altitude").
Is that a fault or normal?  Is the software maybe evaluating between distance, actual altitude and battery level?
If so it should IMO not be doing so, because the "safe tree sector altitude" in my area is about 45m. Fortunately on its 100m travel inbound the homepoint there were no trees...
Any ideas?

Try the experiment again with same distances & altitudes, but having the battery fully charged. If the drone still doesn't climb to 50 m but flies straight back at 38 m, then I guess it's a faulty behaviour.
If by contrary it climbes to 50 m as RTH altitude states,  then it means DJI has built a clever algo that gives priority to returning home if the battery is low (17%), without reaching the requested RTH altitude.
go,

One possibility is the last item in the RTh section of the manual (page 15).
It says:
If you move the throttle stick (left joystick) after the aircraft rises above 65 ft but below the preset Failsafe RTH altitude, the aircraft will stop ascending and immediately return to the home point.

Quest-So Posted at 2017-1-14 12:40
Try the experiment again with same distances & altitudes, but having the battery fully charged. If the drone still doesn't climb to 50 m but flies straight back at 38 m, then I guess it's a faulty behaviour.
If by contrary it climbes to 50 m as RTH altitude states,  then it means DJI has built a clever algo  that gives priority to returning home if the battery is low (17%), without reaching the requested RTH altitude.
go,

I see your point and thought so, too.
But initiating the "Smart Return Home" with a full battery would mean that you had to fly the "full half way distance" (straight line from the Home Point), that would result in a distance of about 4.5 km (15,000 ft) with approx. 60-50% battery
So initiating "Smart Return Home" within technical limits (max. distance 2.5 km)  would be possible with approx. 40-30% battery. Within lawful limits (Europe = 500 m) only at 30-20% battery life.
In my test the P3P was 100 m away (flying outbound) when the battery dropped from 18% to 17% when "Smart Return Home" was initiated . As it takes 10 seconds to start "Smart Return Home" from its initiation, the distance was then 200 m. The P3P turned inbound and returned home at its current altitude...

Labroides Posted at 2017-1-14 15:04
One possibility is the last item in the RTh section of the manual (page 15).
It says:
If you move the throttle stick (left joystick) after the aircraft rises above 65 ft but below the preset Failsafe RTH altitude, the aircraft will stop ascending and immediately return to the home point.

You are possibly right.
I also took a look inside the actual manual (Phantom 3 Professional User Manual v1.8_20160719.pdf), and was irritated by the fact that this RTH section is still a mess, because it still mixes up two different things:
it describes "Smart RTH" as being the process of pressing the RTH button and "Low Battery RTH" of being the self RTH initialization during "low battery in regard to distance" situations. (The Failsafe RTH description on RC signal loss is o.k.)
But by ignoring the handbook the user learns that pressing the RC's or app's RTH button triggers the manual initialization, and activating "Smart Return Home" (Smart RTH) in the app arms the RTH in case of "low battery in regard to distance" situations.
In order to avoid further confusion by continuing to read the manual, I missed the part you mentioned.
I took a close look again at the app's flight record playback and I noticed this:
at 100 m distance and 32 m altitude (not 38 m as I mentioned before) the battery dropped from 18 to 17%. In this moment "Smart Return Home" initiated. I continued to fly outbound (right stick forward 35%) in a long right turn (left stick 10% right). After 10 seconds the "Smart RTH" started by decelerating, turning right home sharply, accelerating and maintaining 32 m altitude.
I took my hands off the controls in the moment when the "Smart RTH" started. I relased the left stick at about 5% down (unintentionally but maybe caused by wearing wind gloves), what in the end must have caused staying at 32 m (instead of climbing to 50 m as the set RTH altitude).  

So as the manual describes under "Failsafe Safety Notices" on page 15: having the throttles in an other position than 0% ("moving the throttle stick)" during RTH operation, causes the RTH being executed at the current altitude, when the drone is already ascended above 20 m and is still below the "pre- set Failsafe RTH altitude".

So the behaviour is correct by the manual, but one has to be aware of the fact that when flying a climb or descend (between 20 m and the pre-set RTH altitude) when "Smart RTH" is actually started, the drone will "stop ascending" (keep the current altitude) as fixed during the return home flight...

vr-pilot Posted at 2017-1-14 23:06
You are possibly right.
I also took a look inside the actual manual (Phantom 3 Professional User Manual v1.8_20160719.pdf), and was irritated by the fact that this RTH section is still a mess, because it still mixes up two different things:
it describes "Smart RTH" as being the process of pressing the RTH button and "Low Battery RTH" of being the self RTH initialization during "low battery in regard to distance" situations. (The Failsafe RTH description on RC signal loss is o.k.)

"this RTH section is still a mess, because it still mixes up two different things:
it describes "Smart RTH" as being the process of pressing the RTH button and "Low Battery RTH" of being the self RTH initialization during "low battery in regard to distance" situations. "

What makes you say that the manual is wrong, that 'smart RTH' is not when you press the button or icon ?

DJI have defined 'smart RTH' as the process of either using the RTH button on RC, or the RTH icon on the display. It's only a name. And by their definition the 'smart' bit seems to be that you can control the position of aircraft using the RC sticks to avoid objects as it returns to home.

Aardvark Posted at 2017-1-15 05:18
"this RTH section is still a mess, because it still mixes up two different things:
it describes "Smart RTH" as being the process of pressing the RTH button and "Low Battery RTH" of being the self RTH initialization during "low battery in regard to distance" situations. "

The manual still describes "Smart RTH" as being the process of pressing the RTH button while a so called "Low Battery RTH" being the self initializing RTH in "low battery in regard to distance" situations.
BUT FOR THE ACTUAL HANDLING OF THE DRONE THE FOLLOWING IS TRUE:
Pressing the RC's or app's RTH button triggers RTH instantly on demand, while activating "Smart Return Home" in the app options just arms the RTH for "low battery in regard to distance" situations.

The manual's description is wrong and confusing, because there literally is no "Low Battery RTH" to be found in the usage of the P3P...  (That causes conflicts in the use and understanding of the term "Smart RTH/Smart Return Home".)

"while activating "Smart Return Home" in the app options just arms the RTH for "low battery in regard to distance" situations. "

If that is true then the problem would be that the control switch in the App' needs a name change from "Smart Return-To-Home" to something more meaningful like "Low level battery RTH"

That would then clear up any confusion surely.

"because there literally is no "Low Battery RTH" to be found in the usage of the P3P... "

This extract from the P3P manual seems to describe "Low Battery RTH" quite well.

The aircraft should RTH when it hits the yellow 'H' marker (Power required to return home) at the start of the 'low level battery warning' yellow marker on the battery timeline.

Aardvark Posted at 2017-1-16 07:36
"while activating "Smart Return Home" in the app options just arms the RTH for "low battery in regard to distance" situations. "

If that is true then the problem would be that the control switch in the App' needs a name change from "Smart Return-To-Home" to something more meaningful like "Low level battery RTH"

What you describe is what I meant:
generally RTH can be called "smart", sure. The problem: what is called "Low level battery RTH" in the manual is called "Smart Return-To-Home" in the app. This again collides with the term "Smart RTH" in the manual which just stands for pressing the RTH button on the RC or in the app.

The most definite solution would be, as you mentioned, to rename "Smart Return-To-Home" in the app to "Low level battery RTH".
This way the three terms "Smart RTH", "Low level battery RTH" and "Failsafe RTH" would be used comprehensible...

vr-pilot Posted at 2017-1-16 12:54
What you describe is what I meant:
generally RTH can be called "smart", sure. The problem: what is called "Low level battery RTH" in the manual is called "Smart Return-To-Home" in the app. This again collides with the term "Smart RTH" in the manual which just stands for pressing the RTH button on the RC or in the app.

Thank you for your input, I've never used RTH other than the odd test session in the field, just to make sure all worked as it was supposed to. One that I'd not got round to was checking the function of the "Smart RTH" icon in the App' (battery never too low to RTH when flying).

I've just noticed, on the IOS version at least, that when "Smart Return-To-Home" is disabled it pops up a note.....I'll need to do some more testing .

The important bit is being aware of it and the consequences.

A suggestion to DJI perhaps to get the icon renamed.

Aardvark Posted at 2017-1-16 13:34
Thank you for your input, I've never used RTH other than the odd test session in the field, just to make sure all worked as it was supposed to. One that I'd not got round to was checking the function of the "Smart RTH" icon in the App' (battery never too low to RTH when flying).

I've just noticed, on the IOS version at least, that when "Smart Return-To-Home" is disabled it pops up a note.....I'll need to do some more testing .

An other example for the confusing use of terms by DJI is the "F-Mode" (Function Mode).
Also known as:
Intelligent Orientation Control (IOC), Multiple Flight Mode(s), Intelligent Flight Modes, Intelligent Navigation... (there may be more).
The P3P manual (still) contains quite some of those ambiguities, partially e.g. caused by copy and paste from Inspire 1 manual functions which are/were non existent for the P3P...

Seeing these handbook bugs never corrected and changes in function and operation badly documented (if ever) is showing that this field is not a core interest of DJI.
Something which can be problematic when using a product commercially and an official request can not be answered clearly due to handbook flaws.
Here DJI has to take some considerable action IMO, if "PRO" should stand for what professionals (and officials) expect.