I'm a complete newbie to drones, so if this is a dumb question, please be kind.
Let's say I'm at sea level, and I take my M4P up to 400 feet, I fly over a hill which is 300 feet high, and I have a RTH occur. My settings are to go to 200 feet upon RTH. Since the drone is over a 300 foot hill, what will it do?

The drone will return home at the current altitude of 400ft,   all altitudes the drone understands are related to take off point.      The drone will not drop to the RTH altitude only climb to it if it's lower.  

If you lower the drone to below 300 feet after flying over the hill it will crash into that one. If the drone stays higher than 300 feet it will RTH at that height.

Always set the RTH height to higher than any obstacles.

In this case if the hill is 300ft higher than your take off position then set RTH height to around 350ft (to allow for trees etc and a safety margin).

As others have said, if the drone is higher than that 350ft when RTH starts it will not descend but will return at current height. If it is lower than the 350ft AND further than 20m horizontally from your take off point then it will climb to 350ft before heading home.

Note also that if the RTH is because of loss of signal, the aircraft will retrace part of it's flown course (I don't remember how much - 50m maybe?) to try to regain signal before returning.

To understand what happens in various situations with your new drone, head out to a big, open area with no obstacles around and experiment in that safe environment. That way you get no surprises and can plan where you fly knowing what the drone might do.

DAFlys Posted at 2-17 01:59
The drone will return home at the current altitude of 400ft,   all altitudes the drone understands are related to take off point.      The drone will not drop to the RTH altitude only climb to it if it's lower.

Thanks. That is good to know.

_SoP_ Posted at 2-17 02:30
If you lower the drone to below 300 feet after flying over the hill it will crash into that one. If the drone stays higher than 300 feet it will RTH at that height.

Thanks for your reply.

No Original Thought Posted at 2-17 02:46
Always set the RTH height to higher than any obstacles.

In this case if the hill is 300ft higher than your take off position then set RTH height to around 350ft (to allow for trees etc and a safety margin).

Thank you. I think that your advice about going to an open area and playing around is a good idea. I live in the middle of a forest with 100' tall trees, and the only thing that I've done is to go up to 400', circle around a little, come back down, and go up and down my road. I'm still learning how to control the drone, and I'm being very cautious.

Cautious is good.
Forget about height above sea level, it only becomes important when you are taking off from high mountains. From the manual
"Max Takeoff Altitude [3]
With DJI Mini 4 Pro Intelligent Flight Battery: 4000 m
With DJI Mini 3 Series Intelligent Flight Battery Plus: 3000 "

Unless close to the ground or the top of an 'obstacle'  and within range of the downward looking sensors, the drone know ONLY its height relative to the take off point and that is all 'it thinks about'.

Sean-bumble-bee Posted at 2-17 12:49
Cautious is good.
Forget about height above sea level, it only becomes important when you are taking off from high mountains. From the manual
"Max Takeoff Altitude [3]

Thanks for your reply. I have another question about maximum height above the take off point. The maximum height that is allowed in the USA is 400’, so does that mean that I can not fly to the top of a hill that is 500’? Although I would only be maybe 100’ above the hill, I would be 600’ above my take off point. How does one resolve this?

You can fly to whatever height you want, UNDER 1640ft * relative to the take off point, PROVIDING a 400ft long string tied to the drone CAN touch the ground DIRECTLY beneath the drone.
If the string CAN NOT touch the ground directly beneath the drone then, as a US hobby pilot, you are breaking FAA rules.


* DJI has placed an hard ceiling height limit of 1640ft /500m in the drone's firmware. That can not be broken unless the firmware is hacked or the drone malfunctions.

Sean-bumble-bee Posted at 2-17 14:16
You can fly to whatever height you want, UNDER 1640ft * relative to the take off point, PROVIDING a 400ft long string tied to the drone CAN touch the ground DIRECTLY beneath the drone.
If the string CAN NOT touch the ground directly beneath the drone then, as a US hobby pilot, you are breaking FAA rules.

Oh, that is so good to know. Thanks for your reply. So, I would just set my maximum altitude higher than 400'. Should I just set it to 500m and keep an eye on my altitude? What do others do?

J Hawk Posted at 2-17 16:31
Oh, that is so good to know. Thanks for your reply. So, I would just set my maximum altitude higher than 400'. Should I just set it to 500m and keep an eye on my altitude? What do others do?

I would suggest that you should set the maximum height and RTH height to the lowest that each flight needs i.e change them for each location.
An excessive max height leaves the door open to, either by accident ( as has happened to me ) or design, setting an excessively high RTH height and that wastes power in the climb to RTH height ( if needed ) and the descent from RTH height.
It may also influence the low battery percentage threshold.
In addition it may put the drone up into high wind.
Setting the max height low also reduces the change of you breaking the 400ft string rule ( AGL ).

Sean-bumble-bee Posted at 2-17 17:20
I would suggest that you should set the maximum height and RTH height to the lowest that each flight needs i.e change them for each location.
An excessive max height leaves the door open to, either by accident ( as has happened to me ) or design, setting an excessively high RTH height and that wastes power in the climb to RTH height ( if needed ) and the descent from RTH height.
It may also influence the low battery percentage threshold.

Sounds like a good idea. Thanks again.

Hi, J Hawk. Seems your concern is already answered. Additionally, you can refer to the Mini 4 Pro user manual. Please use this link: https://dl.djicdn.com/downloads/ ... _User_Manual_EN.pdf.  Have a great day.

DJI Tony Posted at 2-18 00:22
Hi, J Hawk. Seems your concern is already answered. Additionally, you can refer to the Mini 4 Pro user manual. Please use this link: https://dl.djicdn.com/downloads/DJI_Mini_4_Pro/20240115/DJI_Mini_4_Pro_User_Manual_EN.pdf.  Have a great day.

Yes, when in doubt, read the bloody manual.

J Hawk Posted at 2-18 01:25
Yes, when in doubt, read the bloody manual.

You got it. Thank you for choosing DJI. Have a nice day.

J Hawk Posted at 2-17 22:52
Sounds like a good idea. Thanks again.

Sean-Bumble-Bee mentions a lot of good points! Set your max altitude for the area you are flying in high enough so that if the drone loses signal connection with the controller, and returns to home on its own,  it will clear the tallest obstacle with room to spare.
As he mentioned, you don't want the drone to ascend higher than it needs to, and run into high winds aloft, drain the battery, or worse yet not be able to make headway.
If the drone still has a connection to the controller, but begins an auto return to home due to it  calculating you are close to the point of no return with the battery, and then attempts to climb higher and runs into a strong headwind, the calculation will be off and you may not have sufficient battery to make  it back home.
If that ever happens, don't push it to the limit and have the drone decide to force land. Pick a spot you know you can  safely land and find the drone, and land and go get it.
The Mini 4 has collision avoidance and if your return to home is set too low to clear an obstacle, so long as the drone see's the obstacle, it will attempt to go around it or over it, and continue to return to home.
The plus side of a high set return to home altitude, is often the drone will regain connection to the controller as it ascends.
The  Mini 4 has an AR return to home feature, and if you have this enabled  in settings, the drone has a look at your AR homepoint and if it thinks there are no obstacles in the way, it won't ascend to the return to home altitude if it doesn't think it needs to, it will calculate a path straight back and decend once it gets closer, and continue to land if you let it.
But collision avoidance is far from perfect, and low light, thin wires and branches, and non reflective  objects, as well as a few blind spots results in the possibility of a collision, so don't rely on it. I've found the Mini 4 Pro very good at  avoiding obstacles it's approaching head on, and while the Mini 4 has some sideways avoidance, it has a blind spot above it and also below to the rear, so just keep that in mind and all is good.
Collision avoidance does not work in very low light or in the dark!
I've  been flying my Mini 4 with the Integra goggles, and yesterday I was  cruising down this gully in some hills and the Mini 4 lost connection with the goggles, and did a failsafe return to home, which is a goggles  thing. The drone flew towards the hill blocking the signal and went up  and over it in a nice smooth motion. I was impressed and a smile of confidence appeared on my face.

Manitobahunter Posted at 2-18 09:04
Sean-Bumble-Bee mentions a lot of good points! Set your max altitude for  the area you are flying in high enough so that if the drone loses  signal connection with the controller, and returns to home on its own,  it will clear the tallest obstacle with room to spare.
As he  mentioned, you don't want the drone to ascend higher than it needs to,  and run into high winds aloft, drain the battery, or worse yet not be  able to make headway.

Thanks for all the good info. I really appreciate it.

J Hawk Posted at 2-18 11:45
Thanks for all the good info. I really appreciate it.

You're very welcome!

As Tony said RTFM!!! The information you seek is in it under the RTH section. And MUCH better than any answer you have received here.