MAVIC FLY AWAY AND DJI CASE ANALYSES

[AlanTheBeast]

Since the signal did not reconnect, it's very unlikely that it cleared the building and made it to those trees.

It was (presumably) flying northward. If it hit the south side of the building then falling into the trees on the south side of the building is possible.

 

[HFMan]

The red line is "above ground", so as the ground level falls from 1075 to 1010 m ASL, the red line will follow that at 38 m above ground.

And there is the problem with your analysis. RTH does not follow a trajectory 38 meters above the ground. It will start at 38 meters above the ground at the last known point, and STAY at that altitude (roughly 1113 meters above sea level) the entire distance until it reaches the home point.

 

[AlanTheBeast]

And there is the problem with your analysis. RTH does not follow a trajectory 38 meters above the ground. It will start at 38 meters above the ground at the last known point, and STAY at that altitude (roughly 1113 meters above sea level) the entire distance until it reaches the home point.

I never said the drone follows the ground at 38 m or along any "trajectory". That is what Google Earth does when you set a line relative to the ground going back to the HP. Google Earth has no clue as to what is being done.

• the building ground is at 1075, and
• the Home Point is at 1010, and
• the drone was RTHing at 103, then

the height above ground at the building is 38m. 1075 + 38 = 1113. So there is nothing wrong with my analysis - allowing that we don't know how well the building is rendered - certainly the rooftop mechanical rooms are not.

The fact that the "above ground height" of the red line in GE at some distance away is lower is irrelevant.

 

[HFMan]

Would you agree that the RTH height would have been roughly 103 meters above the ground at the home point? If so, then it indeed changes the rendering and is not irrelevant. If his Mavic had maybe been just 5 meters higher at signal loss he very well might have made it. Your rendering would have it still smacking into the building. I'm just pointing out that your rendering is misrepresenting the actual scenario by not accounting for a constant RTH height.

 

[HFMan]

To put it more succinctly, what is the altitude of the red line at the home point in your rendering?

 

[AlanTheBeast]

To put it more succinctly, what is the altitude of the red line at the home point in your rendering?

Irrelevant. That is just a tool to draw a straight line from where the HP is and where the drone was. At the start of that line the terrain is the same ASL (1075 in the Esplanade and 1075 at the base of the building on the south side).

What is relevant is how high above the ground (1075m ASL) the drone was (38m AGL) which is 1113m (ASL). Does that sound familiar?

What you don't appreciate is that the "sea" is 1000 km from Brasilia and the earth is not only not round it is not even a spheroid. It is a punch of sections like a soccer ball that each are spheroidal but different from each other. So using Google Earth's ASL's and then its projected "absolute" altitude at a random location will not give you an accurate height above ground at that location.

But, using local differences in elevation from G.E. will be quite accurate. IOW, the HP altitude in GE might be off by +7 metres. But being so close, everything in the area would be off by +7 metres.

0 Error: 1075 - 1010 + 38 = 103.
+7m error: 1068 - 1003 + 38 = 103.
​

Regardless, we have no idea what the real projection of that building should be.

 

[BerndM]

I came up with the same problem in the Home Altitude being 200 feet BELOW the disconnect point altitude and when you put that 10 story building in the way, you have a major problem.
HOWEVER, I think you MIGHT have survived that discrepancy if not for THIS very serious problem. Did you realize what was on the top of that building???? A VERY TALL and high power radio transmitter antenna. This alone could easily have overwhelmed the poor little DJI even if the frequencies they were using were nowhere near what the Mavic uses.
Here's a picture of the antenna


I think your flight was doomed right from the start.

Given the extra height of that big antenna, I think you may have crashed into the antenna.
You should get permission to check on the roof of that building. Your Mavic may hopefully be waiting for you up there.

 

[AlanTheBeast]

Would you agree that the RTH height would have been roughly 103 meters above the ground at the home point? If so, then it indeed changes the rendering and is not irrelevant. If his Mavic had maybe been just 5 meters higher at signal loss he very well might have made it. Your rendering would have it still smacking into the building. I'm just pointing out that your rendering is misrepresenting the actual scenario by not accounting for a constant RTH height.

My RTH redline height is constant in the vicinity of the building and that is what is pertinent.

The Esplanade is at 1075 m per GE.
The building grounds are at 1075 m per GE.
He's 38 m above the ground. Period.

1075 - 1010 + 38 = 103
​

And yes, the drone might have been climbing following.

But he was descending at 0.2 m/s at the last received data point. Since his programmed RTH was at 30 m (1040), the drone would maintain its altitude at the time that RTH began.

And of course, the building shown in GE is not rendered correctly. The mechanical buildings on top put the top even higher. So the drone ended on the south side of the building on the ground in my projection or on the south side of a mechanical room (or another rooftop obstacle) in yours.

 

[AlanTheBeast]

I came up with the same problem in the Home Altitude being 200 feet BELOW the disconnect point altitude and when you put that 10 story building in the way, you have a major problem.
HOWEVER, I think you MIGHT have survived that discrepancy if not for THIS very serious problem. Did you realize what was on the top of that building???? A VERY TALL and high power radio transmitter antenna. This alone could easily have overwhelmed the poor little DJI even if the frequencies they were using were nowhere near what the Mavic uses.
Here's a picture of the antenna
View attachment 10820

I think your flight was doomed right from the start.

Not only that but the mechanical rooms which are not correctly rendered in GE.

The RTH is indeed set "below ground" level in the vicinity of the Esplanade, but that's not relevant as the drone will maintain its altitude at the time that RTH began. I don't think he got over the roof, mind you. I think he smacked the south side of the building.

 

[HFMan]

Alan- I give up... you don't seem to understand the incorrect slope of your line can change everything, while you claim it is irrelevant. The path his Mavic would have taken would NOT be the path you have rendered- not even close. Carry on, I know exactly what I am doing and sick of you pointing out I do not. Either way, it doesn't matter at this point, his drone is lost.

 

[AlanTheBeast]

Alan- I give up... you don't seem to understand the incorrect slope of your line can change everything, while you claim it is irrelevant. The path his Mavic would have taken would NOT be the path you have rendered- not even close. Carry on, I know exactly what I am doing and sick of you pointing out I do not. Either way, it doesn't matter at this point, his drone is lost.

Sorry. You're correct - there is a slope. I assumed it would remain parallel to ground level. I just looked at it from the side which I should have done earlier (attached).

That said, it would hit one of the mechanical rooms on top of the building or vent or antennas ...

Also note that the drone was descending when RTH began, so it would have been lower than the last height in the log.

And we do not really know how high that building actually is.

His drone may in fact be up on that roof.

 

[HFMan]

Yes- we now agree!

 

[HFMan]

In addition to the large antenna that BerndM pointed out, there are also other tall masts on that building.

 

[AlanTheBeast]

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

Fernando should pay the building manager a visit.

 

[AlanTheBeast]

Yes- we now agree!

You could have saved a lot of BW with your GE skills by simply presenting the same side view that I did above. So obviously it's all your fault.

 

[AlanTheBeast]

Um....the first amendment is copied in below for your reference...think you might be confusing the first amendment (colloquially known as freedom of speech) with perhaps another thing...certainly this doesn't seem like it applies to drones, I'm sure you'd agree...

Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.

Have you picked up on the fact that the flight in question was in the city of Brasilia which is in ....

 

[Cyberpower678]

Have you picked up on the fact that the flight in question was in the city of Brasilia which is in ....

No clue where it's in.

 

[AlanTheBeast]

No clue where it's in.

Sorry - need your logs.

 

[Cyberpower678]

Sorry - need your logs.

You need my logs for geography lesson? `

 

[AlanTheBeast]

You need my logs for geography lesson? `

Mainly I'm just nosy.