P4 disconnected in flight, found with battery missing

[WBN3]

From the information you've shared so far, it sound like the remote controller disconnected and the Phantom crashed into a tree when it tried to return home. If you upload your TXT flight log here and post a link back here, I'd be happy to review it and confirm/deny that.

I had uploaded to HealthyDrones, but it didn't have all the details that this does, so thanks for the link. The log for the flight in question is here. I was really referring to the file stored on the drone itself, which should contain more information about what happened after it disconnected until it lost power. As far as I know, it won't be possible to retrieve that file without power on the drone.

For comparison, the log of the flight immediately prior (just minutes before) is here. On that flight, Go to Home was activated at 2m 29s, and it shows the craft stopping forward motion, ascending to 246 ft., then continuing flight toward home. That altitude is consistent with what my son had programmed - 70 meters (even though the units on the app are set in Imperial, the selection for RTH altitude is in Metric). He disengaged Go to Home and flew it in Sport and P-GPS most of the way back, but that brief period of flight in Go Home mode indicates to me that the RTH altitude was set correctly.

On the flight he lost the drone, it shows the drone essentially hovering and decreasing in altitude after the return to home mode was activated. The drone was on the ground only a few minutes between those flights, and my son says he didn't change the RTH altitude. Is there a way to find the actual setting of that in the flight log? When I open the app and look at that setting currently, would it be accurate when not connected to the drone?

Appreciate the help!

 

[BudWalker]

@WBN3
You could try to remove the internal SD card like this pilot
.DAT file for the P4?

I don't own a P4 so I can't say how tricky this would be.

 

[WBN3]

@WBN3
You could try to remove the internal SD card like this pilot
.DAT file for the P4?

I don't own a P4 so I can't say how tricky this would be.

We won't be opening the case since we're still looking for warranty coverage and I'm pretty sure that would void it. But thanks for the info.

 

[WBN3]

From the information you've shared so far, it sound like the remote controller disconnected and the Phantom crashed into a tree when it tried to return home. If you upload your TXT flight log here and post a link back here, I'd be happy to review it and confirm/deny that.

Did some data analysis of those two flights... I am more comfortable with graphs, so here are pictures to illustrate what I commented on earlier.

This is the full first flight of the day. Four parameters plotted are altitude (left axis, ft.), speed (right axis, mph), battery (right axis, %) and an indicator when Go Home is activated (green line).

Here is the part of that flight where Go Home was activated (there were two downlink gaps in the data). You can see that altitude increased as expected and forward speed was resumed. This graph is on slightly different scales to match with the plots for the second flight.

Here is the full flight where the drone was lost... time on the x-axis is in minutes of flight, which picks up from the preceding flight.

Here is the last minute of data to zoom in on altitude and battery... wouldn't have expected it to suddenly start trying to land at 43% battery, but wondered if there was any correlation. The step-wise decrease in battery percentage is just because the value is reported without decimal places... in reality it was a slow, steady decrease.

It is clear to me that the drone behaved differently on the second flight than the first, and it isn't obvious that the change in altitude was correlated to activation of Go Home... this makes me wonder if there was an operational issue that caused it to lose altitude. I am less concerned now that there was an erroneous Go Home altitude set in the app, since the altitude did go up for a bit after Go Home was activated. I've looked at the other values recorded in the log and don't see anything that closely correlates to altitude decrease, but there's a lot I don't understand about the data.

 

[BudWalker]

Did some data analysis of those two flights... I am more comfortable with graphs, so here are pictures to illustrate what I commented on earlier.

This is the full first flight of the day. Four parameters plotted are altitude (left axis, ft.), speed (right axis, mph), battery (right axis, %) and an indicator when Go Home is activated (green line).

Here is the part of that flight where Go Home was activated (there were two downlink gaps in the data). You can see that altitude increased as expected and forward speed was resumed. This graph is on slightly different scales to match with the plots for the second flight.

Here is the full flight where the drone was lost... time on the x-axis is in minutes of flight, which picks up from the preceding flight.

Here is the last minute of data to zoom in on altitude and battery... wouldn't have expected it to suddenly start trying to land at 43% battery, but wondered if there was any correlation. The step-wise decrease in battery percentage is just because the value is reported without decimal places... in reality it was a slow, steady decrease.

It is clear to me that the drone behaved differently on the second flight than the first, and it isn't obvious that the change in altitude was correlated to activation of Go Home... this makes me wonder if there was an operational issue that caused it to lose altitude. I am less concerned now that there was an erroneous Go Home altitude set in the app, since the altitude did go up for a bit after Go Home was activated. I've looked at the other values recorded in the log and don't see anything that closely correlates to altitude decrease, but there's a lot I don't understand about the data.

The GoHome isn't being triggered by the battery state, it's being triggered by the App. Possibly by the RC Signal Lost being set to Return-to-Home in the app.

In the second flight

Here the green background denotes a flyCState of GoHome. If the smart battery system were telling the P4 to go home that would be shown in the SMART_BATTERY.goHomeStatus value but the value is NonGoHome. However, the OSD.flightAction has a value of AppAutoGoHome indicating it's the app telling the P4 to go home. I looked at the .csv (using Excel ) and noticed there were some dropouts starting around time 852.

In the first flight there was a similar situation.

Like the second flight the SMART_BATTERY.goHomeStatus value is NonGoHome indicating that it's not the battery telling the P4 to go home. The OSD.flightAction has a value of OutOfControlGoHome which is different from the second flight.

Is the RC Signal Lost set to Return-to-Home? This is shown in the App. If so that would be a likely explanation for the behavior of the two flights.

 

[WBN3]

The GoHome isn't being triggered by the battery state, it's being triggered by the App. Possibly by the RC Signal Lost being set to Return-to-Home in the app.

In the second flight
View attachment 72173
Here the green background denotes a flyCState of GoHome. If the smart battery system were telling the P4 to go home that would be shown in the SMART_BATTERY.goHomeStatus value but the value is NonGoHome. However, the OSD.flightAction has a value of AppAutoGoHome indicating it's the app telling the P4 to go home. I looked at the .csv (using Excel ) and noticed there were some dropouts starting around time 852.

In the first flight there was a similar situation.
View attachment 72175
Like the second flight the SMART_BATTERY.goHomeStatus value is NonGoHome indicating that it's not the battery telling the P4 to go home. The OSD.flightAction has a value of OutOfControlGoHome which is different from the second flight.

Is the RC Signal Lost set to Return-to-Home? This is shown in the App. If so that would be a likely explanation for the behavior of the two flights.

Yes, the RTH option is selected for RC Signal loss. In the second flight, the Go Home was manually triggered by my son. As I'm sure you saw in the initial start-up message, there is a general aviation airport about two miles away. The craft reached the boundary displayed on the app for the restricted flight region around it and began flying along the boundary rather than continuing on the heading he had been flying. When he realized what was going on, he triggered Go Home.

My concern was the behavior once Go Home was activated (regardless of what triggered it). That was not the same between the two flights. My comment about the battery was really to address whether it had reached the critical low level where auto-landing would be triggered.

 

[BudWalker]

Yes, the RTH option is selected for RC Signal loss. In the second flight, the Go Home was manually triggered by my son. As I'm sure you saw in the initial start-up message, there is a general aviation airport about two miles away. The craft reached the boundary displayed on the app for the restricted flight region around it and began flying along the boundary rather than continuing on the heading he had been flying. When he realized what was going on, he triggered Go Home.

My concern was the behavior once Go Home was activated (regardless of what triggered it). That was not the same between the two flights. My comment about the battery was really to address whether it had reached the critical low level where auto-landing would be triggered.

I don't quite see what you're talking about when you say the behavior was different. The only significant difference I can see is the altitude gain and then drop in the second flight. Both flights loiter for 10 - 20 secs at the start of goHome while the P4 yaws around to point home. It's hard to tell how long the loiter is because of the dropped packets.

 

[WBN3]

I don't quite see what you're talking about when you say the behavior was different. The only significant difference I can see is the altitude gain and then drop in the second flight. Both flights loiter for 10 - 20 secs at the start of goHome while the P4 yaws around to point home. It's hard to tell how long the loiter is because of the dropped packets.

The uncommanded loss of altitude in the second flight (while in Go Home mode) on a trend that would put it into the trees within the next minute is exactly what I'm talking about. It should've continued ascending to the programmed altitude (70 meters - 246 ft). I'm sure that's why we lost the bird.

 

[msinger]

My concern was the behavior once Go Home was activated (regardless of what triggered it).

Both flights were in different directions -- the last was closest to the Baytown Airport. Your last flight log shows the Phantom started automatically descending about 33 seconds before RTH was manually initiated. There is no indication of this in the flight log, but I can only assume the Phantom was automatically descending since it flew into restricted airspace.

 

[WBN3]

Both flights were in different directions -- the last was closest to the Baytown Airport. Your last flight log shows the Phantom started automatically descending about 33 seconds before RTH was manually initiated. There is no indication of this in the flight log, but I can only assume the Phantom was automatically descending since it flew into restricted airspace.

Home point is in the opposite direction from the restricted space. The app wouldn't let it fly into the restricted space, which is why my son triggered Go Home. There was a decent breeze blowing the day this happened, but how would that affect it? Once Go Home is activated, I would have thought it would ascend (which it was trying to do at first) then fly home. It's like it hit a conflict in the command code that over-rode the ascend-then-fly-home instruction. If the wind was pushing it in the direction of the restricted space, could it somehow cause it to auto-land? Why isn't there any warning message about the restricted space landing? There is plenty of data after all the changes being discussed before the RC lost contact with the drone.

 

[WBN3]

Both flights were in different directions -- the last was closest to the Baytown Airport. Your last flight log shows the Phantom started automatically descending about 33 seconds before RTH was manually initiated. There is no indication of this in the flight log, but I can only assume the Phantom was automatically descending since it flew into restricted airspace.

And where do you see indication that it was "automatically" descending?

 

[msinger]

Home point is in the opposite direction from the restricted space.

It doesn't matter where the home point was marked. Your son's Phantom was flying toward the restricted airspace.

Why isn't there any warning message about the restricted space landing?

Before taking off, DJI GO did warn your son that he was about to fly in a warning zone (which has no flight restrictions). He took off and flew directly toward the airport until he hit the restricted altitude flight zone at 13m 48s in the flight log. From that point until 14m 8s in the flight log, he continued to attempt to fly toward the airport with the right stick in the full up position. Instead of pressing forward, the Phantom stopped and auto descended at its current location. While there is no message in the flight log indicating what happened, I can only assume the Phantom was trying to descend to a safe altitude since it was in a restricted altitude flight zone.

And where do you see indication that it was "automatically" descending?

The Phantom descended on its own 97.5 feet between 13m 48s and 14m 17s in the flight log.

 

[WBN3]

It doesn't matter where the home point was marked. Your son's Phantom was flying toward the restricted airspace.

Okay, I just don't understand the way it behaved because it yawed around from -96 deg. to 90 deg. 5 seconds after RTH activated (pointing back toward Home) and then began ascending toward RTH altitude while holding station 1 second later. There were no inputs from the RC - he was completely allowing it to function on auto. It ascended for 4 seconds then began descending again (all while pointed away from the restricted zone with no inputs from the RC).

 

[msinger]

I have never intentionally tried to fly into a no fly zone to see what would happen. Perhaps DJI support can help you.

 

[WBN3]

I have never intentionally tried to fly into a no fly zone to see what would happen. Perhaps DJI support can help you.

We have a case open with them... they've reviewed the flight log and are sending a pre-paid shipping label to send it to their repair facility. I just wanted to understand what happened. If they say it was pilot error, I want to know what the error was. My son didn't fly it into the restricted zone, but has launched from within it before. He is a cautious pilot, but needs to learn from his mistakes (if he made any). Those flights reached an altitude higher than this flight, and it was never forced to land. There are two zones shown on the map (one red, one yellow). He was outside the red zone (no fly) but within the yellow. If this behavior is part of the programming of the app, or something in the firmware of the drone, we need to know.

 

[msinger]

My son didn't fly it into the restricted zone

On the final fatal flight, he did in fact fly into a restricted altitude flight zone. That doesn't explain why the Phantom started to auto descend on the edge of that zone though. According to the Phantom manual, it seems that should not have happened.

 

[WBN3]

On the final fatal flight, he did in fact fly into a restricted altitude flight zone. That doesn't explain why the Phantom started to auto descend on the edge of that zone though. According to the Phantom manual, it seems that should not have happened.

Where can I find a map of the flight restricted zones? Is it only available in the app, or are they published by FAA?

 

[msinger]

You can find DJI's no fly zone map here.

 

[WBN3]

I found that one, but it only shows the "airport" radius for the no-fly zone... appears to be a glitch in the page, because I tried both Chrome and Internet Explorer and neither shows the larger radius. However, on that page there is a link to this map.... It does show the boundary which he reached on the second flight of the day. What's interesting is he has taken off and flown within the Authorization Zone (larger radius) around Baytown Airport before (at a local park), but never tried to cross the boundary. That flight reached a higher altitude (186 ft.) and never generated any sort of a forced landing or even a different warning (only the same one on start-up as the flights on Christmas Day). The only difference is he never used the Go Home feature.

This wiki page is hard to decipher, but appears to have some useful info as well. It doesn't use the same zone descriptions as the map pages, but has an illustration of how the altitude limit slopes up from 66 ft. at the edge of the no-fly zone up to a limit of 1640 ft. at the 1 mile radius which designates the edge of the second (authorization or restricted-altitude flight) zone. He was outside the second zone, and even if he was a few feet inside it, his ceiling ought to have been well above the altitude he was flying on the second flight.

 

[WBN3]

You can find DJI's no fly zone map here.

Forgot to hit the "Reply button"... see my comments above.