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Poorly Documented RTH Feature - Auto Land if < 20m from Home Point
3462 15 2015-5-13
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david.p.mann
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Based on a number of first-hand experience posts in the Inspire 1 forum (and the Phantom 3 forum), it is clear that there is a very poorly documented (and intentional) behavior of the Return to Home (RTH) function of which many pilots are unaware and which could potentially result in a crash and loss of your aircraft.

Poorly Documented RTH Behavior:  As documented ONLY in the Inspire 1 Release Notes under Major Updates, Item 6: "Aircraft automatically descends and lands if RTH is triggered when the aircraft flies within a 20 meter (65 foot) radius of the Home Point."  However, this specific RTH behavior is NOT documented anywhere in the Inspire 1 Owner's Manual.  

Apparently, this RTH behavior has been part of the Inspire 1 firmware since the January 15, 2015 firmware update (v1.2.0.16).  However, the Inspire 1 Owner's Manual (2015.3 version) would lead operators to believe that if a Return to Home (Smart RTH or Failsafe RTH) is triggered, the Inspire 1 will:  either a) rise to the RTH height input in the DJI Pilot app, or b) remain at current altitude if it is higher than the programmed RTH height; then fly directly back to the current Home Point; and then slowly descend and land.  If there is a different behavior than this when the Inspire is less than 20 meters (65 feet) from Home Point, it is not addressed in the latest version of the Inspire 1 Owner's Manual.

CONFUSION:  There is a setting in DJI Pilot App in MC Settings > Advanced Settings > RC Signal Loss, which would appear to let you determine what action should be taken if RC Signal Loss occurs:  Return-to-Home or Landing.  If Return-to-Home is selected, then, in my opinion, the Inspire should return to home even if the Inspire is less than 65 feet from current Home Point.  REQUEST: Can several Inspire 1 pilots please carefully confirm whether or not this is the case?  I cannot currently test this as my Inspire is being repaired.

MAJOR CONCERNS:  Imagine if you are in a small open area (e.g., your back yard, or a client's outdoor property adjacent their building, a park, etc.) with trees, structures, streets, buildings, etc., all around you and you are currently flying over any of these structures. If you are less than 65 feet from the current home point (e.g., your take-off point) and you initiate a RTH or the RC loses connection with the quadcopter or a low-battery RTH is automatically initiated, the Inspire 1 will immediately start descending and attempt to land at its CURRENT POSITION!  Clearly, if this happens, you are at high risk of crashing/damaging your expensive Inspire and possibly damaging property.

Here are more examples of where this RTH behavior within 65 feet of Home Point would be unexpected/unwanted and possibly result in a crash and loss of the aircraft:
- You are flying out over water (or a client's building or your house) with a nearly full battery less than 65 feet away and you lose RC connection to the Inspire for any reason, or, a low-battery RTH is initiated.  Do you want the Inspire to immediately descend and land where it is in this situation - NO!
- You are flying over a creek, or the side of cliff, or over a client's expensive equipment or facilities less than 65 feet away from Home Point and connection to the Inspire is lost, or, a low-battery RTH is initiated.  Do you want the Inspire to immediately descend and land where it is in this situation - NO!
- You are within 65 feet of home point and are flying only a few feet above ANYTHING other than an unoccupied/safe clearing with a battery that has more than a 30% charge level and you lose RC connection to the Inspire, or, a low-battery RTH is initiated.  Do you want the Inspire to immedately descend and land where it is in this situation - NO!

This current RTH behavior when the Inspire is within 65 feet of Home Point is the same as what would happen if the Critical Low Battery level was reached -- that is, the Inspire 1 will automatically start descending and land where it is.  This makes sense for a Critical Low Battery condition, but NOT for a RTH that is initiated by either the user or the Inspire's firmware when the battery has greater than the critical charge remaining.

When I initiate a RTH and there is sufficient battery power to get the craft home, I would ALWAYS want the Inspire to: first rise to the programmed RTH height, then return to hover directly over the currently defined home point, and then slowly descend and land.

DJI - PLEASE change the RTH behavior to in all cases (including when aircraft is within 65 feet of Home Point) be as described in the Inspire Owner's Manual on page 13 for Smart RTH, and on page 15 for Failsafe RTH.

Smart RTH (Page 13 of Inspire 1 Owner's Manual)
Using the RTH button on the remote controller(refer to “RTH button” on P28 for more information) or the RTH button in theDJI Pilot app when GPS is available to enables smart RTH. The aircraft returnto the latest recorded Home Point, you may control the aircraft's orientationto avoid collision during the Smart RTH. Press the Smart RTH button once tostart the process, press the Smart RTH button again to exit Smart RTH andregain the control.







2015-5-13
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lethbrp
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Like you said, I am one of those who was unaware of this functionality. Thank you for raising this issue. I agree, it should always rise the the height limit set and return to home (if sufficient power).
2015-5-13
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paul
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This accounts for the behaviour I experienced when testing the RTH height setting after updating to the latest firmware and IOS Pilot app. I can confirm that the Inspire starts to descend in its current location but that you can stop the descent by applying power. I thought it was through the RTH setting showing zero in the app but subsequent tests of RTH with the craft more than 20m away had "normal" behaviour.

Thank you for your post...all is explained.

I agree this "feature" is  a risk to safety and the security of the craft.
2015-5-13
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f1
lvl.3

United States
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A workaround might be to start one's flight in a clear area more than 65 feet from the primary activity.  
2015-5-13
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Captain Obvious
Second Officer

Australia
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f1@frankschaffe Posted at 2015-5-14 09:58
A workaround might be to start one's flight in a clear area more than 65 feet from the primary activ ...

This makes sense.....
2015-5-13
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Outta Control
lvl.3
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I tested the RTH just yesterday and here are my observations.

As noted, if you are within the 65m space and you RTH the Inspire, I witnessed the UAS maintain its altitude (less than what I set it) and landed the craft at the take off point. At that point I was very curious and concerned about this so Launch the UAS and went beyond the 65m space and upon hitting the RTH the craft went up to the altitude that I've set on the app and returned home like it was supposed to.
2015-5-13
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Mike-the-cat
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Outta Control Posted at 2015-5-14 13:04
I tested the RTH just yesterday and here are my observations.

As noted, if you are within the 65m s ...

20m OR 65 feet. NOT 20m. Thanks.
2015-5-13
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Mike-the-cat
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It is common sense that you should NOT fly in an area where you cannot sight the aircraft. If you are such an advanced flyer  that you are going to take off from a building / closed space then caveat emptor.

On page 3 of version 1.2 of the English version of the Inspire Quick Start Guide, it is clearly stated:

● Environmental Considerations:
2. Only fly in open areas. Tall buildings and steel structures may affect the accuracy of the onboard compass and GPS signal.
3. Avoid from obstacles, crowds, high voltage power lines, trees or bodies of water.


If the above is complied with: then landing at a distance from home is completely logical as it provides a margin of safety for the Inspire landing on top of you or on you. It is a question of which is the lesser of evils. Losing a craft is better than maiming someone, agree?

That unlikely situation could occur in a catastrophic  situation when:
1. the controller non-functional despite the craft being in plain sight.
2. there is a possible loss of GPS signal
3. you are incapacitated and cannot run away from the home point to avoid being struck by the returning aircraft

In respect of the instructions provided in the operating manual, examples #1, 3 you provided represent actions that are in clear contravention of provided instructions. You are welcome to violate them (and many do) but as stated earlier, caveat emptor.

In the case of an accidental or malicious RTH trigger within 20m from Home, you can regain control of the craft by flicking to ATTI (as you, an expert commercial flyer knows).

For condition #2, the user is tempting fate with risky behaviour. Again, caveat emptor.

I would agree that in the full user's manual, the behaviour of RTH within 20m should be clarified (it was in earlier Phantom manuals). The programming was well intended and I think, should be defended for what its original design intent was.
2015-5-13
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Abe
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I agree with you that the documentation can be very confusing. I've read it many times and there are so many corner cases where RTH functionality differs from what you might expect that I find it difficult to know what to actually expect. But in all honesty, I've been flying DJI aircraft for over a year -- both Phantoms and Inspires -- totaling 100+ flights, and have never used RTH for any reason. The only time I needed it it sadly didn't work and my Phantom 2V+ flew away and I never found it. Nevertheless, I view RTH as a last resort, and certainly not something I'd use or worry about within 65 feet of takeoff.
2015-5-13
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w1der
Second Officer

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I would NEVER EVER use the RTH function if the Inspire where in line of sight ... to much at risk ...
As a lot of accidents is in fact caused by these features I think it is called for to change the setup for some of them ...

Auto land on battery emergency ...
I want the option to turn this off completely as I am better at doing a "safe" crash landing manually than the auto pilot will ever be!
This should be optional as a less experienced pilot might be better of letting the software land the Inspire.
And as some one else said before ... I would rather damage ONLY one battery (from draining it completely) instead of crashing the entire bird.

RTH when signal is lost ...  
The inspire should travel to pre set altitude "always" ... If necessary, work it´s way home but when it has reached the home position it should maintain hovering as long as possible and wait to see if the bird and remote is able to bind again before initiating auto land!

Also I would like to be able to remove the Auto take off and Auto Land buttons from the screen in the pilot app and replace them with more useful commands ...

What do you guys think about this ?  


2015-5-13
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w1der
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Mike-the-cat Posted at 2015-5-14 14:00
It is common sense that you should NOT fly in an area where you cannot sight the aircraft. If you ar ...

"In the case of an accidental or malicious RTH trigger within 20m from Home, you can regain control of the craft by flicking to ATTI (as you, an expert commercial flyer knows)."

If the RTH is because of loss of signal this wouldn´t help much ...
Do you know if this works when the software initiate an emergency landing because of battery warning ?
2015-5-13
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david.p.mann
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Lot's of good discussion here - which is a key benefit of good users forum.  Thanks everybody for your comments and feedback.

I raised this discussion topic primarily because a behavior of a key operating/software "safety" feature -- Return to Home -- of the Inspire and P3 when flying it within 65 feet of Home Point is not documented in Owner's Manual.

The primary concern for experienced flyers would be what happens on unexpected loss of RC connection when flying within 65 feet of Home Point.  Granted, the I1 or P3 should not lose connection this close to the RC and yet, following the latest firmware update, there are reports on this forum of pilots experiencing screen blackouts and RC disconnects when flying the I1 well within its operating range in open terrain. I don't know if this has occurred within 65 feet of Home Point, but we should consider that the possibility exists.

As experienced flyer, we all need to understand exactly how our quads are going to perform under a variety of circumstances.  My point was this particular performance behavior is not well documented. If I have RC connection to the quad, I can switch to ATTI mode if a RTH is triggered.  But if I lose RC connection and an RTH is triggered, then I have no fall-back control options.  In this situation, I need to know exactly what the craft will do - when it's more than 65 feet away and when its less than 65 feet from Home Point.

Hats off to "F1" for his recommendation to start a flight (or otherwise set a Home Point) in a clear/safe area that is at least 65 feet distance from planned target flight area for those situations when you would not want the I1 to auto land anywhere in the target flight area. This would be a prudent procedure to use, for example, when doing video aerial inspections of nearby structures (e.g. roofs) where the pilot is typically standing (at ground level) within 65 feet of the building.  Of course, with this strategy, it would be wise to place cones or tape off the Home Point landing area (or post an assistant in that location) to keep others away in the event the I1 goes into RTH mode and you, the pilot, cannot quickly return to the "remote" Home Point landing area.
2015-5-14
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gergefil
lvl.1

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This is quite serious. You can start flying on the beach and while you are on the sea and distance less than 20m if you lose signal, it will land right into sea.

I wonder of this also applies to P3. Again, this is quite serios.
2015-6-12
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david.p.mann
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gergefil Posted at 2015-6-13 05:11
This is quite serious. You can start flying on the beach and while you are on the sea and distance l ...

YES - with current firmware as of June 12, 2015, both the Inspire 1 and the Phantom 3 will land where they are if a RTH is initiated with the aircraft within 20 meters of the recorded home point position.
2015-6-12
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FoxSTI
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This is crazy, mostly because RTH will activate if you loose signal.
2015-6-12
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