Hi, one of my team members ran into an issue with their Air 2s that caused it to crash. In short, they launched on 30% battery, received a notification of the battery being critically low at 10%, and accepted the RTH prompt. The drone was not very far away and still within line of sight, but after it was over halfway back it suddenly turned left, and ultimately crashed with 8% battery left. I have their write-up below for what happened in their words, and I have the flight log that I will link to.

Would somebody be able to help me translate the flight log to figure out what happened to make it crash? Was it opperator error, a battery error, a RTH glitch? I would like to avoid a future crash like this down the line.

https://www.phantomhelp.com/logviewer/7NY0M36YLLR2LSQP6IFG/

Date of Flight: November 22nd

Location: Eastville VA

Environment: open flat field near a residential house and body of water

55 degrees and sunny; 2mph wind NW

During my flight on November 22nd at roughly 3 PM I received a notification that the battery was nearing ‘critical low’ (10%) with a prompt to return to home and land. I immediately agreed ‘yes’ to this operation. I stood by and waited for it to return, with eyes on it in the sky. When the drone was over halfway to the home point, it veered off course and took a hard left, before plummeting to the ground from a 100 or so feet off the ground. In the time in began going off course, I began moving toward it with eyes still on it, to get a better look at what was happening. I did not touch the controls to intervene. The area in which it landed was in front of the house to the right of a short clump of dead trees. It did not hit the trees (they were not in the path of home), but rather fell 10 feet from them.

I'm not sure if this is noteworthy but, in the previous flight that day I received the same ‘return to home’ prompt at 17% and landed safety. However, during this 2nd flight I was not prompted until 10% battery. I’m not sure why it didn't prompt earlier but when it plummeted it was at 9% battery.

RTH altitude adjusted to 101m with 30% battery is very bad think.

LoveYou Posted at 12-6 12:32
RTH altitude adjusted to 101m with 30% battery is very bad think.

Agreed, it's not ideal. My question is, although not ideal nor advisable, is that what ultimately caused the crash?

How did the battery get to 30%?
The low cell voltages and low battery temperature early in the flight suggest that it may have been sitting around for some time discharging.

It was a mistake to launch with a battery that indicated only 30%.
It was a bigger mistake to launch with a battery that had been sitting around discharging, as the % indication is only accurate with a freshly charged battery.

At 1:00.9 with the right stick pushed full forward, the battery cell voltages are below the critical low voltage level of 3.2 volts.
There was a warning of this at 1:01.5 .  Battery power limit will automatically reduce the aircrafts mobility to ensure flight safety.
The drone should have been brought back at that point.

The operator continued flying until reaching 11% at 4:44 when the following message appeared on the screen:
BCritical low battery. Aircraft landing automatically (Code: 30033).; Critical low battery. Aircraft landing automatically.
Despite this warning, the operator continued to fly further away from the home point, taking it from 82 feet to 190 feet while it was in critical low voltage autolanding.

At 5:05.3 and 103 ft from home, the descent speed increases and the drone began tumbling downwards.

When the drone was over halfway to the home point, it veered off course and took a hard left
The drone's movements match the joystick input - it went where the operator directed it.

before plummeting to the ground from a 100 or so feet off the ground.
It started falling from 41 ft.

In the time in began going off course, I began moving toward it with eyes still on it, to get a better look at what was happening. I did not touch the controls to intervene.
The drone began falling at 5:05.3.
The operator was still making full stick inputs until 5:06.2.
The drone hit the ground at about 5:07.4.

Was it operator error, a battery error, a RTH glitch?
It wasn't a battery error and the drone was never in RTH because it was in critical low voltage autolanding.

I would like to avoid a future crash like this down the line.
Make sure your operators only commence a flight with a freshly charged battery and never with a battery that has been lying around discharging.
They need to pay more attention to warning messages and battery voltages.

not that it has anything much to do with the crash (the flight log experts will chime in shortly), you don't have to "agree" to the rth prompt for it to take action, i think it will kick in by itself unless you tell it not to.

rth is not an excuse for the drone to fly all by itself with no pilot behind the controls.  if you have a connection with the drone using your remote controller, you need to remain in control of the drone and guide it if you can, or cancel the rth if you need to, or pause it if you must but at a minimum you need to monitor the controls as the pilot in control.  no one holding the remote controller should watch a drone fly out of control unless the remote controller is ineffective (i guess the logs will tell).  if you are disconnected, the rule is to try to get re-connected as quickly as possible so you can take control.  doesn't mean you can't let the drone ultimately return home and land by itself but it  does mean you have to be ready to take the wheel.  this goes for manual rth, battery low rth, or disconnect rth.
for example, i don't like it when the drone has to rise to my set altitude (nearly 350 feet) just to return home....if it doesn't have to.

sorry to hear about your unfortunate crash.  i would never take off with a battery under 50%.

eta:  i see the analysis has already begun so my comments may not be relevant.

I may be mistaken but I see no sign of an RTH being commanded, a bit worringly nor do I see a warning that there was only enough battery left to get home.
Starting a 4:44, 11%  there are warnings that the drone has reached critical battery level and is descending yet your pilot continue to use the sticks to manoeveur the drone horizontally including flying away from the home point 4:45 to 4:59. It continues to follow stick commands until it perhaps hits the trees.
Sorry but this would be pilot error in my book. I would be over the home point  and or low before the drone got near 10%

Two points not related to the crash, both the RTH height and the Maximum height are VERY high. If the drone has to climb to RTH height then an excessive RTH height wastes energy in both the climb and descent. The maxiumum height may well be WELL above the legal height limit for drones where you are

Sean-bumble-bee Posted at 12-6 14:19
I may be mistaken but I see no sign of an RTH being commanded, a bit worringly nor do I see a warning that there was only enough battery left to get home.
Starting a 4:44, 11%  there are warnings that the drone has reached critical battery level and is descending yet your pilot continue to use the sticks to manoeveur the drone horizontally including flying away from the home point 4:45 to 4:59. It continues to follow stick commands until it perhaps hits the trees.
Sorry but this would be pilot error in my book. I would be over the home point  and or low [view_image]before the drone got near 10%

I really appreciate all of the insight. It was supposed to be a simple practice flight but it's clear it was poorly planned/executed and the team member was not ready yet to fly on their own. It's helpful to have the errors that occurred confirmed for training purposes moving forward.

Just to confirm, had the drone been in either RTH or Auto Landing mode without pilot interference, would the sticks have not registered as being maneuvered? AKA, am I correct in reading that the only way that the sticks show as guiding the drone is for the pilot to be controlling and manipulating them?

JJBarnes_0101 Posted at 12-6 15:56
I really appreciate all of the insight. It was supposed to be a simple practice flight but it's clear it was poorly planned/executed and the team member was not ready yet to fly on their own. It's helpful to have the errors that occurred confirmed for training purposes moving forward.

Just to confirm, had the drone been in either RTH or Auto Landing mode without pilot interference, would the sticks have not registered as being maneuvered? AKA, am I correct in reading that the only way that the sticks show as guiding the drone is for the pilot to be controlling and manipulating them?

had the drone been in either RTH or Auto Landing mode without pilot interference, would the sticks have not registered as being maneuvered? AKA, am I correct in reading that the only way that the sticks show as guiding the drone is for the pilot to be controlling and manipulating them?
The recorded flight data shows any joystick input from the operator.
No input and nothing shows.
If sticks are moved, the data shows how much and in what directions.

With regards to the sticks and RTH, the sticks remain effective in controlling the drone to some extent and how big an extent depends of the drone model and one or more of the software versions (App and or firmware version).
You would need to read the relevant manual and posts here or Mavic Pilots to get better details.

With some drones, the stick-movements vs effect-on-an-RTH may have been very quietly changed in either an App Update or a firmware update.
With my mini etc. once the drone is above a certain height and still climbing to RTH-height a throttle movement ( partial closing?  ( I can't remember for sure)) will terminate the climb and start the flight home. But I think, in some drones, with more up to date software, I recollect that 'messing' with the throttle now CANCELS the RTH and quite a few people seem, or seemed, unaware of that.

With regrards to auto landing, the sticks remain effective but LOTS of throttle is required to keep the drone at a given height or even more throttle is required to make it climb. The response to pitch and roll commands is significantly reduced i.e. horizontal flight speed are significantly reduced.
Incidentally I would suggest that it isn't a bad idea to occasionally bring a drone over the landing spot and let it hover until critical battery landing starts and then experiment with the controls just to see/experience the changes in response/performance, it is marked.

People have flown drones until past/'below' zero percent but that is something that should only be done as a last resort e.g.. they have been 'caught short of battery' over water and it's either fly and possibly damage the battery or sink and ruin/lose the drone and battery. It's probably NOT GOOD for the battery and if pushed too far the voltage may fall low enough for the drone to literally stop the motors in mid air.

Hi there, we are sorry to know about the accident. We recommend that you start a case through the link below and send the drone in for diagnosis and repair. If there is a doubt about the accident, data analysis can also be applied as long as the drone is within the warranty period. http://www.dji.com/support

Hi,

In addition to the given analysis by others, some info about battery. (see my charts of your data)

In flight at 14.8s 1 battery cell reaches a really low value of 3.099 Volts.
Only for very short moment, so no warnings on the screen.
Why so low ? Battery temp at start 19 degrees centigrade (wich is not really low).
Could be a 'bad' cell in the battery.
At this point RC 100% UP stick command ; high power demand = high amps = drop in voltage, but normally not that low!

At 1m00.8s all 3 cells below 3.3 volts; following message on the screen
"Battery power limit will automatically reduce the aircrafts mobility to ensure flight safety"
This low voltage for cell3 only for 0.9 second, that is why at this point no critical low landing was initiated by the sofware.

At 4m 43s warning " Critical low battery | Aircraft landing automatically"
At 11% battery level and with cell voltages : 3.488 | 3.473 | 3.447.

At 4m55.4s wiyth 10% battery level "Battery power limit will automatically reduce the aircrafts mobility to ensure flight safety"
All battery cells > 3.3 volts.

DJI does warn us on time before the really critical values are reached in the cells. (wich is good ofcourse!)The moment the cell battery are below 3.0 volts  than the power to the drone is really really reduced, so speed and controlling height in an critical low batt landing gets difficult!

Your battery showed normal values for rest of the flight, cell values normal compare to battery flights started from 100% to low battery.
Only just after start low cell values, wich is not normal battery behaviour. Just keep an eye on the cell values next flights.
And, i agree with others...

• best to start each flight with full battery
• start with a non-full batt at start ; check cell values and listen and react to the warnings.
• Always land your drone before an automated critical low battery landing!
  

cheers
JJB