MAVIC FLY AWAY AND DJI CASE ANALYSES

[FERNANDO]

Using your first post on the matter as inspiration I looked at GE for ground truths.
Looked at the log for the last height above Home Point.

So:

Home Point "0": 1010 m ASL
Height at loss of connection: 103 m AHP ("Above Home Point") = 1113 m ASL
Ground at building on south side: 1075 m ASL
Height above ground at building: 1113-1075 = 38 m

Red line in my GE rendering is set at 38m above ground.

The only thing that I don't have confidence in is the actual height of the building in GE.
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DJI's reply regarding OA ineffectiveness would apply too. Either because the building is white and/or the brick pattern could cause aliasing resulting in a mis-estimation of range.

And even if we take your rendering which seems to "graze" the roof, that leads to a high probability that it struck something - like the incorrectly rendered rooftop mechanical rooms or ventilation equipment, etc.

View attachment 10811​

I appreciate your help, guys.
I believe it would be physically impossible to the aircraft hit the building. According to the national urbanization act (Brazilian law), the buildings in that area (site of the incident) have a maximum height of 30 meters. We don't need to go to the law, though, if you google the question you'll find out that the average height of a 10 floor building is 30 m (3 meters for each floor).
Then, it's certain that the aircraft was at least 8 meters above the building, high enough not to crash into it.
what do you think?

 

[Kilrah]

That the antennas sticking on top of the building are still there.

 

[Michael Ainsworth]

Listen to the experts. At least check out where they suggest.
Can't hurt. You may be surprised.

 

[Flawless]

I appreciate your help, guys.
I believe it would be physically impossible to the aircraft hit the building. According to the national urbanization act (Brazilian law), the buildings in that area (site of the incident) have a maximum height of 30 meters. We don't need to go to the law, though, if you google the question you'll find out that the average height of a 10 floor building is 30 m (3 meters for each floor).
Then, it's certain that the aircraft was at least 8 meters above the building, high enough not to crash into it.
what do you think?

Read the rest of the thread.

In summary:

You instructed the Mavic to descend, and it was doing so at the point of signal loss. The Mavic would continue to descend for up to five seconds until it initiated RTH. It wouldn't ascend again, as it is at/above RTH height (compared to starting altitude). It then reoriented and Returned Home - either into the side of the building or something on the roof (if it had cleared the building, you would likely have regained signal shortly after).

Conclusions: Pilot Error, geography lesson not required.

 

[FERNANDO]

The most likely thing that he would hit is the mechanical room.

Fernando should pay the building manager a visit.

some more questions: what does the information below mean?

preparing to return - the aircraft prepared to return but did the RTH procedure really start?

RC GPS Num: N/A rcGPS Valid:N/A - how can the aircraft return home if there is no GPS available?



considering that the aircraft is probably on the top of the building, why did the app show the disconnected point as the place where the drone is when I went there to look for it?

 

[HFMan]

We don't know for sure what happened after the disconnect. Remember- you lost signal, so what happened afterwards is NOT in the log. GPS was not lost, the signal between your Mavic and the RC Controller was lost. We are guessing (a very good guess) that after a few seconds the Mavic initiated a RTH procedure and proceeded to try to come home. That is what we have been trying to tell you all along- it probably started to come home, but it ultimately ran aground either on top of the building, or hit the side of the building.

 

[Huskerfan]

Can u borrow a friends drone and fly it over there to see if it's on top of the building? Don't fly too low [emoji14]

 

[Capra Vecinului]

(Not trying to hijack the topic - I just read through the entire thread to see whether there's something to learn out of others' mistakes - and suddenly it struck me that I am not sure of what the RTH altitude actually is.
So: What is that RTH altitude that we are supposed to set & check (because it gets reset after every firmware or app upgrade) before every launch? Is it:
a) The AGL altitude at takeoff point, or
b) The AGL altitude at the point where the drone is, when the RTH is triggered?)

 

[msinger]

What is that RTH altitude that we are supposed to set & check (because it gets reset after every firmware or app upgrade) before every launch? Is it:
a) The AGL altitude at takeoff point, or
b) The AGL altitude at the point where the drone is, when the RTH is triggered?)

The RTH altitude is the altitude above the takeoff point. The drone has no idea how high it is above the ground when RTH is triggered.

 

[HFMan]

Since you don't always where the drone is when RTH might get triggered, you have to set it based on your expected flight path. If you know the ground rises as you proceed on your flight path, you would need to set your RTH point to be higher than ALL objects at the highest elevation of your expected path and anywhere in between. It's an educated guess, and as we saw in this thread you have to think about it a bit before you venture out.

 

[delta-101]

Oh great, that should be fun... going to tell the Ministry of Defence you crashed a drone on top of their building!!
OP, hope you find Mavic!

These threads are always make such interesting reading, good to know there are so many members prepared to put in such an effort to help others!

 

[Kilrah]

RC GPS Num: N/A rcGPS Valid:N/A - how can the aircraft return home if there is no GPS available?

rcGPS = the GPS in the remote controller if any, not the aircraft's GPS. The Mavic's remote doesn't have one, so it's normal that isn't available. Nothing to do with your case..

considering that the aircraft is probably on the top of the building, why did the app show the disconnected point as the place where the drone is when I went there to look for it?

You lost connection. The app has no idea what the aircraft did after that, so what you see is the last position it received before disconnection. The aicraft will have moved away from that when attempting RTH, but since you didn't regain signal there's no record of that.

 

[FERNANDO]

rcGPS = the GPS in the remote controller if any, not the aircraft's GPS. The Mavic's remote doesn't have one, so it's normal that isn't available. Nothing to do with your case..


You lost connection. The app has no idea what the aircraft did after that, so what you see is the last position it received before disconnection. The aicraft will have moved away from that when attempting RTH, but since you didn't regain signal there's no record of that.

doesn´t MAVIC´s GPS work like iphone´s GPS? the app "find my iphone", for example, tells you iphone´s current position...isn´t it the same?

 

[Kilrah]

Find my iPhone uses the cellular network to transmit the position. The Mavic uses strictly direct point to point link between remote and aircraft, so if that link isn't available there's no way for the Mavic to say where it is.

That's why some people install GPS trackers on their aircraft. You could also have gone in that area with the remote and potentially got link again supposing the Mavic wasn't completely broken/battery popped out after the crash.

 

[method007]

Like everyone else in the thread, I also agree that it likely hit the building. I would let it go bro.

 

[DroneForceOne]

@FERNANDO

If you need a SAR flight to look after it, just let me know. Received my Mavic today, but, not willing to hit anything with it! HAHA!

 

[slowgojoe]

Office buildings are usually more like 3.5-4 meters each floor, residential would be closer to 3.

 

[ksiads]

Just curious why you chose the flight path you took. Wasn't there any Class B airspace you could've flown over?

 

[DroneForceOne]

Just curious why you chose the flight path you took. Wasn't there any Class B airspace you could've flown over?

Brazil... Probably There is. But if you do fly, nothing happens, until something happens, and they blame you for the existance of cancer and ban drones from flying anywhere.

Thats how it happens.

 

[AlanTheBeast]

@FERNANDO

Did you contact the building manager to go walk the roof?