My P3P crashed, DJI not cooperating

Thank you for your analysis Meta4, its greatly appreciated. I agree with your numbers but the point of confusion still lies in the fact that the logs report an altitude of 54 feet upon impact. There is nothing near the impact location thats 54' tall. I don't understand why such a discrepancy in numbers. If the impact altitude was 54 feet, it didn't rise a whole lot when it rose to 62/65 feet for the RTH altitude. From the operators perspective, this behavior didn't appear to be a RTH, I thought it was interference and spent those critical 9 seconds trying to regain control rather than cancelling the RTH
 
Thank you for your analysis Meta4, its greatly appreciated. I agree with your numbers but the point of confusion still lies in the fact that the logs report an altitude of 54 feet upon impact. There is nothing near the impact location thats 54' tall. I don't understand why such a discrepancy in numbers. If the impact altitude was 54 feet, it didn't rise a whole lot when it rose to 62/65 feet for the RTH altitude. From the operators perspective, this behavior didn't appear to be a RTH, I thought it was interference and spent those critical 9 seconds trying to regain control rather than cancelling the RTH
Interference won't make your Phantom fly away.
It will just cause difficulty getting the Phantom to do what you direct because the signal is swamped.
I don''t know about the altitude but the pressure drop caused by weather may explain it.
Or a badly calibrated IMU can also show altitude drift
In the end though, it doesn't matter.
There were several things that could have been done to save the Phantom.
The Phantom was in visual range and you could see what height it was but brought it down a little rather than climbing higher which would have saved you (if you had cancelled RTH and prevented it going home and landing in the lake).
When the Phantom is getting close to an obstacle, operator confusion or inexperience can lead to a crash.
I think it's a lost cause, trying to find an out.
One to write off to experience and learn from.
 
That's probably the best point: doesn't matter rock or tree. Without intervention, it was going to crash into something. In the OP's defense, 13 seconds is not a lot of time to: (a) discover that RTH is what is causing loss of control and (b) initiate the sequence (via device or RC) to stop the RTH. While there appears to be enough information to call this pilot error, some suggestions for DJI to reduce the likelihood of this occurring:

(1) First and foremost, I see no logical reason for stick movement to stop vertical ascent to the RTH altitude. For stick movement to stop vertical ascent yet the AC still take off on it's course home at a low altitude just makes no sense. I would argue that in many cases, a pilot is going to move the sticks if RTH is initiated unexpectedly. That's a natural reaction to regain control. They need to get rid of that climb-cancel function as the climb should be part of the RTH sequence. If you want to cancel the climb with stick movement, at least don't take off in the direction of home until the stick movement stops and it can resume it's climb to the RTH set altitude.

(2) In addition to the first point, RTH should rise to the set RTH altitude and hover in place for 30 seconds before taking off in the direction of home. If you are already above the set RTH altitude, just hover in place for 30 seconds, then move toward home. This both gives the pilot some time to react and, seeing it go straight up and hover would be a visual indication that it is about to initiate RTH. To take off immediately and cover 200 feet in 13 seconds (potentially at the wrong altitude if you happen to touch the sticks) also doesn't make sense.

Mike
 
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One more suggestion for DJI .... When auto RTH is activated, the video camera should be activated also. This would have been helpful in my case and others too I'm sure.
 
Chris I intended no offense by my comment I was simply stating human nature to fill in the blanks when we encounter an unexplainable scenario. We all do it in high stress situations, nothing personal directed at you.

That said, I do see the point cancelling RTH ascent if you have 20% battery remaining over water and a long flight home. Sometimes you want it to come home now, not in 30s. Should never happen but if it does... I like knowing I can do that. If you read the friendly manual, it's worth while information to know, however dangerous to those that don't.

They should probably change some commands also with leaving beginner mode and this could be one of them imo. Is there any way you can prove it was accurate throughout the flight then read wrong at that moment without warning? That would make me inclined to consider it more of a hardware issue. Barometers get stuck sometimes due to the way they are made. You give em a swift whack and they release. If the barometer got stuck mid flight and you didn't do anything to cause it, they might take more pity on the situation.
 
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It seems most of the flight I was between 65-100 or so feet which sounds about right. It would seem that at the end of the flight, when I was attempting to bring it in to land, it was still registering 60+ feet. I was standing on the swim platform of the boat reaching for it when it took off by itself in the auto RTH mode. That certainly wasn't 60, 50 or even 40 feet. It may have been at 15-20 ft in reality. So it seems the altitude was correct all along but didn't decrement as I was attempting land it, it retained the original altitude reading.
 
So it seems the altitude was correct all along but didn't decrement as I was attempting land it, it retained the original altitude reading.
At what point in this log would you say the altitude started showing incorrectly?
 
If I'm reading the logs correctly, at flight time 16m 9.4s, auto RTH engaged and I lost control of the aircraft. At that moment, I was standing on the swim platform and the drone was maybe 5' above my head approaching for landing. It certainly wasn't at 62.3' as indicated in the logs.
 
Prior to the point where smart RTH took over, the log is indicating your Phantom was 62 feet in the air. Is that not correct either? If it's not correct, at what point prior to that time is the altitude correct in the log?
 
I think the altitude numbers are correct up to where i started bringing it down to land. The picture I posted was taken shortly before I started bringing it down. I checked the exif data and it shows lat/lon but no altitude. It seems to me that as I brought it down, the change in altitude didn't register. I would have grabbed it within seconds if the RTH didin't engage.
 
And, when you descended so you could reach up and grab it, did you go straight down? How far down did you press the throttle? Did you hold the throttle at a consistent position or were you changing the throttle as it came down?
 
I cant recall specifically how I handled the throttle as I was bringing her down. I had her down almost within my reach when it suddenly took off by itself. I now know that was RTH in action. At that point it was maybe 5' above my head as I stated earlier. I don't think it was straight down, I was bringing it to the boat and down at the same time.
 
Got it. So, you were coming back to the boat at an angle -- descending and coming toward the boat at the same time? Rather than flying directly over top of the boat and coming straight down?
 
Can't say for sure if it was a nice even inclined plane approach or a staircase approach but I was bringing it towards the boat and descending.
 
No problem. I'm just trying to figure out how you flew your Phantom back to the boat -- since you did not mention that in great detail above.

Here's what I'm seeing in your flight log:

16m 9.4s: The log shows your Phantom was 62 feet in the air (you confirmed this above).
16m 9.5s: Smart RTH initiated and your Phantom started to climb to 65 feet.
16m 10.5s: You completely let go of the throttle stick (it was in the center position).
16m 13.5s: The throttle stick is pressed slightly down (or bumped?) for 0.2 seconds.
16m 13.7s: You completely let go of the throttle stick (it was in the center position).
16m 14.4s: Your Phantom started flying toward the crash site.

Only 5 seconds passed between the time RTH initiated and your Phantom started flying toward the crash site. During that time, the throttle stick was only partially down for 1.2 seconds. The Phantom's max descent speed is 9.8 feet/s. That means you would have only been able to descend a maximum of 49 feet if the throttle stick was in the full down position that entire time. So, in the best case scenario, it would have been 13 feet in the air at the time it started flying back to the crash site.

Do you have any thoughts on these findings?
 
That sounds about right. I'm 6' tall, the swim platform is about 1' above the water so that appears to be correct. The mystery still remains if it was at a real altitude of 13-15 feet, why do the logs show 54 feet at impact?

You mention a 5s timeframe from when RTH initiated to the time it flew off. Bear in mind, as I stated previously, RTH started when it was already down from 62'. It was almost within my reach when RTH initiated.
 
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The mystery still remains if it was at a real altitude of 13-15 feet, why do the logs show 54 feet at impact?
I think the real mystery is to explain how your Phantom descended 49 feet without you touching the throttle stick.
 
I think I've been very clear that I was bringing it down before RTH initiated. Clearly it wasn't at 62 feet or 54 feet when it crashed as the photo clearly shows the landscape and there are no obstacles at that height anywhere near the flight path.
 
Bear in mind, as I stated previously, RTH started when it was already down from 62'. It was almost within my reach when RTH initiated.
Okay -- let's back up. Perhaps I'm missing something important.

Above, you stated the following:
"I think the altitude numbers are correct up to where i started bringing it down to land."

At what time in your flight log did the altitude start showing incorrect numbers?
 
I have already answered that question. I've looked at the logs and throughout the entire flight, my altitude fluctuated between approximately 106' and 62'. Looking at the photos taken, that looks correct. I have no other way of verifying that data. I then began bringing the Phantom towards the boat and reducing my altitude for landing. As the Phantom approached my location, the RTH initiated and it flew off in pretty much a straight line, hit the rock and cartwheeled into the water. My friend retrieved it within seconds as he was standing nearby. There is absolutely no way it was at 54 feet when it flew off. That would have put it inland in the trees which would have likely resulted in less damage.
 

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