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Mavic Air crash/lost drone

GarthH

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Hey guys,

On Sunday Aug 25th, I was flying over the Myvatn Lake in Iceland. Around 750m out, 3 minutes into the flight, video feed on phone started to cut off, saw warnings about weak signal so was about to turn back but then lost connection permanently. App shows last location as 65.566455, -16.952539, which is in the middle of the lake. Was flying with a full battery. Been flying for several days in Iceland, and this was a quite routine spin around the lake.

Would appreciate if someone could review the logs and let me know what happened – pilot error or drone issue. I was unable to retrieve the drone as that area is not accessible by foot. I have also left Iceland and returned to Canada. I sent an email to DJI Support with these logs. I do not have DJI Care. Was using MAS v2 props.

Regards,
G.
 

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sar104

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Unfortunately this has all the indications of an improperly latched battery. There was no evidence of downlink signal loss until the disconnect, which occurred immediately after going from full forward elevator to a stop. The resulting positive pitch excursion (not recorded due to latency) has been a relatively common cause of battery disconnects if they are not latched.

Pitch.png

Additionally, the DAT file event stream contains several battery connection entries, another potential indicator of a battery connection problem:

130.460 : 8250 [L-BATTERY]get_cell_voltage_callback_ack failed!||​

And so unfortunately the location data are likely correct, and it is at the bottom of the lake.

Worth noting is that the wind was around 30 mph out of the SE, and so even if it had be a link disconnect, it would not have been able to return to the home point.

 

sar104

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@sar104 I have this entry in all of my flight logs. I asked about it a while back and someone (I think it was @BudWalker) said not to worry about it. Just saying it may not indicate a battery connection issue.
That's why I said "potential indicator", especially when it happens just before a disconnect. In this case it's just one of several pieces of evidence.
 
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GarthH

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Thanks guys. The battery clicked in place like it always does.

Is this something that DJI will accept responsibility for (and replace my drone) or am I out of luck?

On a related note: is emailing [email protected] the proper way to get a ticket opened for this type of issue? I reside in Canada, and could not find a way to open a ticket online.
 

The Editor

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Unfortunately this has all the indications of an improperly latched battery. There was no evidence of downlink signal loss until the disconnect, which occurred immediately after going from full forward elevator to a stop. The resulting positive pitch excursion (not recorded due to latency) has been a relatively common cause of battery disconnects if they are not latched.

View attachment 80703

Additionally, the DAT file event stream contains several battery connection entries, another potential indicator of a battery connection problem:

130.460 : 8250 [L-BATTERY]get_cell_voltage_callback_ack failed!||​

And so unfortunately the location data are likely correct, and it is at the bottom of the lake.

Worth noting is that the wind was around 30 mph out of the SE, and so even if it had be a link disconnect, it would not have been able to return to the home point.

How can a battery on a Mavic Air be “Improperly Latched”?
If it is, it simply will not functional/allow the battery to power on since there is a failsafe switch built into the latching mechanism which prohibits improperly seated batteries from functioning.
 

Doppler

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I wouldn't put it beyond the realm of possibility for the battery to be connected and power on the aircraft while still being latched improperly. But the OP has already mentioned that the battery "clicked in place" so this is perhaps a moot point.
 

sar104

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How can a battery on a Mavic Air be “Improperly Latched”?
If it is, it simply will not functional/allow the battery to power on since there is a failsafe switch built into the latching mechanism which prohibits improperly seated batteries from functioning.
Yes - those sensors are supposed to ensure that both latches are in the engaged position. It hasn't completely prevented battery ejection problems though.

I wouldn't put it beyond the realm of possibility for the battery to be connected and power on the aircraft while still being latched improperly. But the OP has already mentioned that the battery "clicked in place" so this is perhaps a moot point.
In pretty much every single case of battery ejection I've seen across all the DJI models, including where the aircraft DAT file showed the voltage drop as the battery disconnected, the pilot has been completely sure that the battery clicked into place properly.
 
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sar104

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Thanks guys. The battery clicked in place like it always does.

Is this something that DJI will accept responsibility for (and replace my drone) or am I out of luck?

On a related note: is emailing [email protected] the proper way to get a ticket opened for this type of issue? I reside in Canada, and could not find a way to open a ticket online.
Without an aircraft to examine they are likely to offer you 30% on a new aircraft.
 
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JAW

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According to post #19 in this THREAD, the Mavic 2 has micro switches which disconnect the battery when the latching buttons are depressed. Would/Could some sort of a malfunction with a micro switch cause the battery to disconnect while in flight? Just wondering..........

OK, I just realized the OP's drone is not a Mavic 2. But there have been enough mysterious disconnects in Mavic 2 crashes for me to wonder about malfunctioning micro switches.
 
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The Editor

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Yes - those sensors are supposed to ensure that both latches are in the engaged position. It hasn't completely prevented battery ejection problems though.



In pretty much every single case of battery ejection I've seen across all the DJI models, including where the aircraft DAT file showed the voltage drop as the battery disconnected, the pilot has been completely sure that the battery clicked into place properly.
I've never seen one on the Air. Doing a search on the forum doesn't seem to yield any results either - although it's not helped by most people find it very difficult to post in the correct section!

The Spark is a different matter - well documented and ultimately redesigned latches, but have never seen one on the Air for the very reason of the battery being open circuit via the safety switch if not seated properly
 

DanMan32

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I've checked what happens with improper latch on my M2. My experience says both latches need to disengage foe the latch warning to appear. One was not enough.
I haven't tested this as I wouldn't know how, but if a battery unlatched during flight, I would hope it would warn only and keep flying.

It appears what's in the logs is data link between AC and battery and not latch issue. Since I believe the data connection is in the middle of the row of pins with + and - on either side, seems an unlatched battery would cause data connection loss before power loss, unless the AC can tolerate power losses for short periods of time.

Battery swell could explain power loss or unlatching. The swell pre-flight could be barely noticeable but become pronounced as it heats up during flight. I have 2 M2 batteries with swelling issues. One is barely noticeable when at 72F, but expands 1mm when at flight temp. The other starts 1mm expands to 2mm.

There's always the possibility something else occurred that didn't get recorded at the Rzc.
 

sar104

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I've checked what happens with improper latch on my M2. My experience says both latches need to disengage foe the latch warning to appear. One was not enough.
I haven't tested this as I wouldn't know how, but if a battery unlatched during flight, I would hope it would warn only and keep flying.

It appears what's in the logs is data link between AC and battery and not latch issue. Since I believe the data connection is in the middle of the row of pins with + and - on either side, seems an unlatched battery would cause data connection loss before power loss, unless the AC can tolerate power losses for short periods of time.

Battery swell could explain power loss or unlatching. The swell pre-flight could be barely noticeable but become pronounced as it heats up during flight. I have 2 M2 batteries with swelling issues. One is barely noticeable when at 72F, but expands 1mm when at flight temp. The other starts 1mm expands to 2mm.

There's always the possibility something else occurred that didn't get recorded at the Rzc.
That's correct - on the M2 both latches seem to need to be off, although if you depress just one of the latch buttons it triggers the error too:

25.771 : 7802 [L-BATTERY][ERROR] BATTERY_STATE_ABSENT||
27.944 : 7911 [L-FMU/LED]action changed. Normal Flash:bat_absent(27)

It doesn't prevent take off though. I don't have a Mavic Air to test, but I assume it's the same.
 

GarthH

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Maybe in future models they can place the battery on top the aircraft or have it inserted from the side.

I got an automated email from DJI saying that they're reviewing the logs. Would be delighted if they replaced it for me but that seems unlikely since I didn't recover the drone. If I do get offered a 30% discount, I'll most likely pass on that, sell the pieces of my kit (controller, 2 batts, etc) and buy a different model later on.
 

GarthH

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DJI got back to me...looks like 30% is the best they can do. Thanks to everyone who helped with the analysis.

Thanks for getting back to us.

We are sorry for the frustrating experience you have had with our product. We also want to figure out the cause of the incident, however, it was not recorded. As you can see the flight record ended at flight time T=02:18, there was no more flight record after that.

There were many possible reasons which would lead to the interruption of the flight record. In your case, there wasn't any warning about the battery appeared during the flight. Moreover, the message of "130.460 : 8250 [L-BATTERY]get_cell_voltage_callback_ack failed!||" didn't indicate any battery issue, either. This message normally appeared during a short flight when the APP failed to read some information of the battery(such as the S/N of the battery), but it didn't mean that it would fail to read the information again when the request was sent later. That was to say, this message didn't prove any product abnormality.

Due to the interruption of the record, the cause for this incident was not recorded, but it was verified from the record that there was no malfunction found before the record was cut off. The aircraft was under your control and responded well, it worked normally before flight record ended. The aircraft showed no signs of a manufacturing defect or malfunction during the whole flight. For your case, it's unable to locate the main reason according to the flight records you provided, we cannot explain the detail of the incident or rule out any possible speculation. As such, we provide the 30% discount for this case.

And we do understand that it's difficult to accept the result and solution. If we could help you get a higher discount, there is no reason why I don't do that for you. Sorry that the 30% off offer is already the best discount we can offer based on the analysis result while obeying the warranty policy. We are unable to offer you any higher.

We greatly appreciate your support for DJI. Please consider if you need the offer and get back to us in a month if you need it.

Should you have more questions, please feel free to let us know.

Thanks for your patience and understanding. Have a nice day.
 
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Doppler

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DJI got back to me...looks like 30% is the best they can do. Thanks to everyone who helped with the analysis.
Thanks for updating us Garth, and sorry to hear a 30% discount was the best DJI could do. But it is at least better than nothing. The "[L-BATTERY]get_cell_voltage_callback_ack failed!||" message is a mystery to me but I agree that it is not an indication of a serious issue or error. If it was, my MA would have been long lost since I get that message repeated a thousand times in each flight log with all three batteries I have.
 
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sar104

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Thanks for updating us Garth, and sorry to hear a 30% discount was the best DJI could do. But it is at least better than nothing. The "[L-BATTERY]get_cell_voltage_callback_ack failed!||" message is a mystery to me but I agree that it is not an indication of a serious issue or error. If it was, my MA would have been long lost since I get that message repeated a thousand times in each flight log with all three batteries I have.
Nice to see a direct confirmation from DJI about that particular error message.
 

MavicFlyer

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Maybe in future models they can place the battery on top the aircraft or have it inserted from the side.

I got an automated email from DJI saying that they're reviewing the logs. Would be delighted if they replaced it for me but that seems unlikely since I didn't recover the drone. If I do get offered a 30% discount, I'll most likely pass on that, sell the pieces of my kit (controller, 2 batts, etc) and buy a different model later on.
Just curious about how that 30% would work...If they give you 30% off of the retail price of the aircraft only, you may want to consider that. nIt appears you got the Fly More Combo, so you would NOT be on the hook for 70% of your original price. You may also want to check what you could actually get for the remaining parts that you have....plus, you may have bought accessories beyond the FMC...just something to think about...good luck!!
 
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spamgnome

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It's always interesting to me why the Air battery is on the bottom. While it might be latched for takeoff, in suppose its within the realm of possibility that the latch fails during the flight. What do folks think about a thin velcro strap to add an additional layer of security to the battery?
 

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