I work for a public safety agency in Southern California.  Currently we fly the Matrice 210 with the Z30 and XT cameras, depending on the mission.  We also fly the Phantom 4 Pro and Sparks, again depending on the mission.  We have been operational since 2017 and we have almost 100 missions completed.  I say this to point out that our team is not completely new to operating UAS aircraft.   

Back in July, we flew the Phantom 4 Pro on what seemed to be a simple mission.  The weather was clear and wind speeds were in the 5-10 MPH range with some gusts up to around 15 MPH.  Nothing really remarkable, and nothing we have not operated in before.  

The Phantom was about 50’AGL and almost directly above the remote pilot who had the controller with him.  The flight was fine for about 2-3 minutes, and the battery had be discharged to about 59%.  The pilot received a “High Wind Warning” on the Phantom, which is sometimes common.  Without any other warning the Phantom completely shut off, fell directly to the ground, causing major damage.  

We sent it back to DJI and paid the $65 for data retrieval.  We are more concerned about the “why” of the crash because of the nature and liability of being a public agency.  Below is DJI’s response:

Thank you for your patience.

This is XXX from the Technical Support team, and I will be assisting you on this case from now on for related inquiries about data analysis.

Here's the result of the data analysis on your case number: CAS-XXXXXXXXXXXXX.

The power shutoff in mid-air due to the high wind environment giving the battery a lot of pressure to maintain the battery in mid air.

We can still proceed with the repair, however, you will cover the repair charges.

Your understanding and cooperation will be highly appreciated.

Best regards,

XXXXXXX

Question:  

Has anyone else had this happen to them?  

Does anyone know why this could have happened?

Did you start the flight with a fresh 100% charge?  Any low battery warnings?

The battery was at about 80% at takeoff.  Absolutely no low battery warning at all.  

"and the battery had be discharged to about 59%"

If your battery had been sitting for over 5 to 10 days...depending on your auto-discharge setting,  then taking off with a battery reading of 59% could easily be the cause.

I am surprised the tech reporting,  did not state the condition of the battery CELLS in his report.  So I believe what the tech is saying, is the CURRENT USE in high wind environment will
draw down the cells much faster....... more wind, more current draw.

a sitting battery that goes into a bird can easily read 59%.......however the moment you take off, you NEED to look at what the cells are reading.  In this case they were most likely 3.4vdc each
or lower.......in all reality the bird should have warned of low battery voltage.......BUT IT DOESN'T DO THAT.... it just runs out of power because the PERCENTAGE of battery is incorrect.

This is why the statement:  NEVER FLY UNLESS YOU START WITH A FULLY CHARGED BATTERY.

Randy

I appreciate the good information regarding the battery.  I do not think I fully explained like I should have, but we did not take off at 59%.  At takeoff we were at about 80%, but you bring up a valid point about having a 100% fully charged battery.  Most of our missions are planned and we normally operate that way but sometimes, depending on the circumstances, we do not.  With the Matrice, we never have launched without two fully charged batteries, all the batteries are marked and always paired.  But there have been issues with the Matrice, and that is another story altogether.   

The 59% battery reading was at the time of the shutdown, with no low battery no warning of any kind.   

The point of my post is to see if others have experienced anything similar and to find out why this happened.  There is nothing in our current written policy that prevents us from launching with less than a 100% charge on batteries.  However, if we learn that we have to change our policy to state that we “should” not or “shall” not launch without a fully charged battery, then we may have to consider that.  

Hi, sorry to know and read about this. We're trying to pull up your case number (CAS) using your DJI Forum account but gave us zero results. Please provide us the associated case number via Personal Message and we'll check and seek further assistance with the designated team. We appreciate your patience.

Note the first question in post #2.  He asked this because we've seen this mistake and this scenario repeated dozens and dozens of times over the years.

I agree with Rwynant and I agree with DJI.  

You must always launch with a fully charged battery.  No exceptions, no excuses.  See the manual.  

There is a critical cell balancing routine during charging which takes place once the charge reaches 100%.  If you fail to fully charge the battery, the cell balancing can't take place.  This promotes the chance for an abnormally low cell voltage in one of the cells during extreme demand and a possible battery shut-down.  Avoid this problem by charging the battery to 100% and the charging process is completed.  

If you wish to launch on a battery that's less than fully charged, it will probably be okay and it might not be okay - it depends on the flight.  But it's at your risk.  

Sorry for your loss.  

DJI Diana I think I just sent you a PM.  

I looked through the manual and I did not find anything that states you should not launch unless the batteries are at 100%.  Not trying to be smart or cute, but can you please tell me what page or what section it is on?

This begs the question(s):
What is the purpose of a battery level indicator if it is not accurate?  
Is it just a “kinda” indicator?  Battery level indicator is a “maybe” indicator?  
Is this acceptable if you are flying in a jet and the pilot is relying on a fuel gauge that is not providing reliable data to the pilot?   

Considering all the advanced technology packed into these advanced aircraft (UAS), it seems to me getting a battery (fuel) level indicator, needs to provide 100% accurate information to any pilot (remote or not), is absolutely critical to any type of commercial operation or even hobbyist endeavor.  

In our case 59% should not mean zero, or even close.  

Falling from the sky with no warning because the battery was drained, while the indicator was reading 59% should not be acceptable to anyone who operates aircraft.

phoenix329 Posted at 8-14 15:02
I looked through the manual and I did not find anything that states you should not launch unless the batteries are at 100%.  Not trying to be smart or cute, but can you please tell me what page or what section it is on?

This begs the question(s):

Top of page 3 under the caption "Battery Use"

https://dl.djicdn.com/downloads/ ... y+Guidelines+En.pdf

Your AC didn't fall from the sky because the battery was drained.  We speculate it fell from the sky due to a particular battery cell that had fallen below the minimum threshold due to high power demand (which was apparently a wind gust, but it could also have been the pilot/controller demanding power combined with the wind gust) during a flight.  Presumably, the high power demand created a voltage lag which exceeded the minimum allowed voltage of a particular cell causing the battery to shut itself off.  

Another complication with this is it has been speculated that launching with a partially charged battery will show a "false reading" on the app.  

You can't say you had no warning.  You already stated you had a wind warning.  A wind warning is a warning.  

The solution to the problem is following the guidance within the battery manual.  That is, you must always launch with a fully charged battery.  The veterans in this forum know this.  Scroll up and see the very first question in this thread up in post #2.

For future reference, another thing that can cause your battery to fail during flight is launching with a cold battery.  Make sure your battery is warm when you launch - at least 20 C.  Make sure it's fully charged.  Those are the two main things to be concerned about.  If your battery is at least 20 C and it is fully charged, your DJI battery will operate wonderfully.

Good luck

phoenix329 Posted at 8-14 15:02
I looked through the manual and I did not find anything that states you should not launch unless the batteries are at 100%.  Not trying to be smart or cute, but can you please tell me what page or what section it is on?

This begs the question(s):

I looked through the manual and I did not find anything that states you should not launch unless the batteries are at 100%.  Not trying to be smart or cute, but can you please tell me what page or what section it is on?
Also top of P57 - Preflight Checklist

This begs the question(s):
What is the purpose of a battery level indicator if it is not accurate?  
Is it just a “kinda” indicator?  Battery level indicator is a “maybe” indicator?  
Is this acceptable if you are flying in a jet and the pilot is relying on a fuel gauge that is not providing reliable data to the pilot?

It is accurate ... if you start with the battery fully charged but is not reliable when you start with a partially charged battery.

Considering all the advanced technology packed into these advanced aircraft (UAS), it seems to me getting a battery (fuel) level indicator, needs to provide 100% accurate information to any pilot (remote or not), is absolutely critical to any type of commercial operation or even hobbyist endeavor.  

Exactly ... that's why you need to start with a fully charged battery.

The power shutoff in mid-air due to the high wind environment giving the battery a lot of pressure to maintain the battery in mid air.
This "explanation" seems highly unlikely.
A very high wind might blow the drone off course or slow its progress, but it doesn't shut down the power to the motors.
DJI make great drones but their communications are not always the best.
Just guessing ... they might have been trying to suggest that working against the wind drained the battery??

We sent it back to DJI and paid the $65 for data retrieval.
I'll give you a proper analysis and explanation of the battery situation and whether or not it was a factor in the crash ... for free.
Just post your .txt flight record that the app saves.
If you need help finding that, let me know if you use an Apple or Android device and I can give instructions.

That is an intriguing case to say the least, I wonder if your battery cell health was the issue perhaps the cells didn't balance charge properly at some point in your charging cycles, being either the last charge you did prior to the accident? Or a charge at some point in between the last charge prior to the accident?

David Martin Graff Posted at 8-14 16:05
That is an intriguing case to say the least, I wonder if your battery cell health was the issue perhaps the cells didn't balance charge properly at some point in your charging cycles, being either the last charge you did prior to the accident? Or a charge at some point in between the last charge prior to the accident?

It's most likely going to be a simple case of the voltage dropping to critical low voltage level because the % indication gives a false impression of battery charge when starting with a partially discharged battery.
Nothing intriguing or mysterious about it.

Indeed.  We've seen it over and over and over again.

Labroides Posted at 8-14 16:31
It's most likely going to be a simple case of the voltage dropping to critical low voltage level because the % indication gives a false impression of battery charge when starting with a partially discharged battery.
Nothing intriguing or mysterious about it.

So what you're saying is the battery was discharged purposely ahead of time before flying or it was partially charged because it was flown prior to the flight in question but just not flown more than a few low double digit % off the original 100% charge?

David Martin Graff Posted at 8-14 16:50
So what you're saying is the battery was discharged purposely ahead of time before flying or it was partially charged because it was flown prior to the flight in question but just not flown more than a few low double digit % off the original 100% charge?

A battery left sitting around will self-discharge after a number of days which can be set with the app.
People charge batteries and don't use them immediately ... they go down and although the % indicator might show 50 something percent, the voltage they can provide is nothing like what a fully charged battery produces when it's flown down to 50%.
They then fly them hard and the voltage drops very quickly and sometimes the drone does too.

It's all about the voltage and the % indicator does not give an accurate reading for a partially discharged battery.

Labroides Posted at 8-14 16:55
A battery left sitting around will self-discharge after a number of days which can be set with the app.
People charge batteries and don't use them immediately ... they go down and although the % indicator might show 50 something percent, the voltage they can provide is nothing like what a fully charged battery produces when it's flown down to 50%.
They then fly them hard and the voltage drops very quickly and sometimes the drone does too.

Flying a battery on a day not 100% to start is poor flight planning and management. I've had over 1,300 flights and not once do I recall did I ever being my day with a flight that wasn't 100% (maybe it dropped into the mid to upper 90% level because of partial discharge or the cells didn't hit 100% on that prior charge?) Most DJI Batteries discharge at 10 days unless you set them to discharge sooner although the Spark you cannot set the batteries to discharge any sooner....

If you think you'll fly two or three flights on 1 charged battery not during that same day then you're asking for trouble, that's just common sense and Flying 101.