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Lost Mavic Air

Simmo

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@sar104

Hey Guys,
My good friend has lost his Air.
He says he had a total loss of connection, and RTH was pressed, but no bird came back.
The log looks like a total disco at 10 minutes odd. I dont think that the AC even got the RTH command, even though he says the device was beeping at him.
He was at 38% battery at the disconnect, but even waiting for 15 minutes, it didnt come back on low battery??
Cam anyone shed some light this please??
(GPS Health only got to 5, is this a problem?)
 

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sar104

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I don't see any problems with the flight until the end. When he flew it into a tree at 4 m/s.

That's my guess anyway, looking at the flight profile and GE terrain data. The aircraft had descended to 12 m AGL (or AWL) and was heading up a 12 m wide tributary, close to the south bank, with thick trees on both sides, at a steady(ish) 4 m/s. At 625.7 s the pilot abruptly increased and then centered the elevator - did he see an obstacle perhaps? Then the record ends 0.5 s later. Downlink was good, and the only thing likely to kill the link like that is a collision. With a couple of tenths of a second latency the actual impact is often not recorded.


2018-08-19_[09-53-10]_01.png

The only other possibility that comes to mind is a dislodged battery, but that looks unlikely in this case.
 
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Simmo

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Thanks mate!
If you watch the video, the link ends when he is right in the middle of that channel.
The top left of his screen said Aircraft disconnected so he says he tried to gain altitude, but could see nothing, so hit RTH.
He says the device started beeping, but then stopped. He hit RTH on the RC but nothing happened?
The AC did not return.
 

sar104

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Thanks mate!
If you watch the video, the link ends when he is right in the middle of that channel.
The top left of his screen said Aircraft disconnected so he says he tried to gain altitude, but could see nothing, so hit RTH.
He says the device started beeping, but then stopped. He hit RTH on the RC but nothing happened?
The AC did not return.

I haven't seen the video. Does it appear to be well clear of the trees on both sides?
 

Simmo

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Dang I should have saved the video when he was here.
Yes, he was in the centre of the creek.
He crossed the main inlet quite high, then rapidly descended into the creek and was (in his words) flying fairly slowly following the up creek .
He was at the logged height by the looks of it, and the video just stops.
Where you could be correct, and something I didnt consider, was if there was a fair latency, he could have flown on into the trees on the southern bank after it disconnected?
I looked at the throttle trace and right on disco, he gave it 100% throttle, that was not apparent on the video.
Nor is any RTH but he says the device was beeping at him.
I'll see if I can get hold of the video.
 

sar104

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Dang I should have saved the video when he was here.
Yes, he was in the centre of the creek.
He crossed the main inlet quite high, then rapidly descended into the creek and was (in his words) flying fairly slowly following the up creek .
He was at the logged height by the looks of it, and the video just stops.
Where you could be correct, and something I didnt consider, was if there was a fair latency, he could have flown on into the trees on the southern bank after it disconnected?
I looked at the throttle trace and right on disco, he gave it 100% throttle, that was not apparent on the video.
Nor is any RTH but he says the device was beeping at him.
I'll see if I can get hold of the video.

Yes - there is sudden full throttle too. Why did he suddenly release the elevator and apply full throttle in the middle of smooth flight? Interestingly, there are a few missed log points at exactly that time.


2018-08-19_[09-53-10]_02.png
 

Simmo

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He says the feed stopped, he noticed that the screen said aircraft disconnected, so simply wanted height, so gave full throttle.
He then hit RTH, which (he says) was confirmed and the device started beeping. This stopped, so he hit RTH on the contoller, which did nothing.
The video shows as you say, fairly smooth flight, in the centre of the creek, then stops.
He knew he had 38% battery left, so hoped for RTH critical battery, but it did not return.
 

sar104

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He says the feed stopped, he noticed that the screen said aircraft disconnected, so simply wanted height, so gave full throttle.
He then hit RTH, which (he says) was confirmed and the device started beeping. This stopped, so he hit RTH on the contoller, which did nothing.
The video shows as you say, fairly smooth flight, in the centre of the creek, then stops.
He knew he had 38% battery left, so hoped for RTH critical battery, but it did not return.

OK - so the video feed stopped, then he centered the elevator and applied throttle, then the data downlink died. That is strange, although those aircraft are somewhat prone to disconnects with their less optimal communications protocol. And if it didn't hit anything then it should have returned home - RTH was set to 30 m, it had plenty of battery and the wind was helping. But it was a Mavic Air, and so if it lost connection it should would have reversed and retraced its flight path for 30 s. Any error in that maneuver could have put it in the trees.
 

Simmo

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I think both do it MrReddog.
The pro doesnt.

@sar104, he is dropping off his Tablet in the morning and leaving it in my letterbox. I will be at work, but at first opportunity, I will upload the video.
(Have you ever had an urge to do one of those random acts of kindness?? Far out this is one of them!! If I were a rich man!!)
 

sar104

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Here's the video.
Obviously uneventful 'til the end, which is the disconnect.

That was pretty tight in there. I'll stick with the suggestion that it disconnected once all that foliage interrupted line of sight, and then most likely clipped a tree while trying to retrace its flight path. I've looked at several logs where the Mavic did the 30 s retrace, and it's often off by a few meters.
 

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Thanks mate! 'Tis sad seeing an old fella so sad!!
But I agree, and I have tried to explain to him that from experiance, generally, DJI, with no fault indicated by the log, say that the AC was performing perfectly up until disco. So accept no responsibilty. As we have seen before, he is not taking that very well....
 

sar104

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Thanks mate! 'Tis sad seeing an old fella so sad!!
But I agree, and I have tried to explain to him that from experiance, generally, DJI, with no fault indicated by the log, say that the AC was performing perfectly up until disco. So accept no responsibilty. As we have seen before, he is not taking that very well....

I'd expect DJI may well offer a 30% discount, and they do occasionally, and seemingly randomly, replace aircraft after events like this, so it's worth pursuing with them.
 

sar104

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Anybody know if the rewind can be set to be a regular return to home, instead? Why would you want it to “rewind”?

On the basis that it will go back to somewhere that it did have uplink from the RC and a direct line home. The downside of the direct return to home is that the reason that it likely lost connection is that it went behind an obstacle, and thus doesn't have a direct line home.
 
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