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MPP RTH obstacle avoidance
199 5 9-10 19:23
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UPTGrad
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Hi.   I have a question I am stumped on.My Mavic Pro Platnum (MPP) flew behind a building, and the signal dropped immediatly.
I quickly lost connection.  It never returned home.
Later, someone called to return the MPP and said it hit the balcony of their hotel room.
It was near the top of the hotel, so my RTH altitude must have been about 30 ft too low.  (Darn!)

I am aware of how quickly one can lose a signal behind a building or trees.   I just misjugged this one.
(I was out flying over the ocean, and never thought of the building as an issue)

I am just trying to figure out why it hit the building when I had all the obstical avoidance stuff turned on.
I know it doesn't have the APAS system like my Mavic 2 Pro.
I was reminded from another post of a possible issue when it's 2000m away (google earth shows it to be almost at this limit)
whereby it flies direcly home.

Any thoughts as to why obstical avoidance failed during RTH when I needed it the most ?
Thank you.
9-10 19:23
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Gimpy
Second Officer
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Only speculation is possible without more information such as a video or log file. The Mavic Pro design (including MPP) only includes forward and downward sensors, so it might have struck something such as the roof or side of the balcony as it returned home. Or, it might not have struck anything initially but lost enough view of the sky to revert to ATTI mode and then drifted until colliding with something on the balcony, but all this is mere speculation. If nothing else, the ATTI mode conjecture can be ruled out or confirmed if you retrieve and post the DAT file found on the aircraft from that flight.

In any case, there are a couple of points that you seem to have misunderstood. First off, "APAS" isn't included with the MPP, though obstacle avoidance (OA) is used unless you had it disabled for RTH. Also, the 2km direct-path-home behavior you mentioned is unrelated to OA / APAS and isn't implemented on the MPP anyway. It has to do with the behavior of newer models, which can partially retrace their route before flying home.

The last point I'd add is that while OA is a nice feature, it's a fallback for manual piloting and isn't meant to be the primary way of avoiding crashes. As you already figured out, your critical mistake (besides flying behind the building) was having an RTH altitude too low to clear the building during the failsafe RTH flight.
9-11 02:35
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UPTGrad
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Gimpy Posted at 9-11 02:35
Only speculation is possible without more information such as a video or log file. The Mavic Pro design (including MPP) only includes forward and downward sensors, so it might have struck something such as the roof or side of the balcony as it returned home. Or, it might not have struck anything initially but lost enough view of the sky to revert to ATTI mode and then drifted until colliding with something on the balcony, but all this is mere speculation. If nothing else, the ATTI mode conjecture can be ruled out or confirmed if you retrieve and post the DAT file found on the aircraft from that flight.

In any case, there are a couple of points that you seem to have misunderstood. First off, "APAS" isn't included with the MPP, though obstacle avoidance (OA) is used unless you had it disabled for RTH. Also, the 2km direct-path-home behavior you mentioned is unrelated to OA / APAS and isn't implemented on the MPP anyway. It has to do with the behavior of newer models, which can partially retrace their route before flying home.

Hi.  Thanks for the feedback.   Yes, it's hard to tell why OA didn't work.
I usually fly in open fields where OA has never been needed to save the day.
I was a little disappointed when the one time I needed it to work, it didn't!  Darn.

Another time, I had some trees come between my Mavic 2 Pro and me, and was really surprised at how fast the signal dropped.  On that aircraft, APAS backed up just enough for me to get the signal back.

That's a great idea on the DAT file.  Maybe I can learn something from that.
I've never looked at it before, so I'll try to figure that out.  Thanks for the idea.

I was recording video on this fateful flight, but unfortunately, that file got corrupted due to the crash.  Darn again.
Thanks again for the feedback.
9-11 04:07
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hallmark007
Captain
Flight distance : 4199094 ft
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When MPP goes into failsafe RTH , it will first rise to Rth altitude set by you it will then fly directly home, if on its return it encounters an obstacle as I believe happened in your case, your craft will stop then climb to clear obstacle I’m not certain as I don’t have manual handy but I think 15 m above obstacle, it will then continue to homepoint, it has know upward sensors so cannot see balcony above it .
I think what may have happened in your situation is MPP stopped for Obstacle it then proceeded to climb but most likely crashed into balcony while climbing to clear obstacle, I have seen this happen a few times with original mavics particularly with trees, since those original mavics dji has changed failsafe Rth procedure , for instance spark will stop at obstacle then back up 15 metres before climbing to avoid obstacles and with mavic air and M2 they operate a retrace procedure.

Hopefully your craft is not to bad, it’s worth knowing exactly what happens with all Rth options and also to set good parameters, good luck .
9-11 04:27
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UPTGrad
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hallmark007 Posted at 9-11 04:27
When MPP goes into failsafe RTH , it will first rise to Rth altitude set by you it will then fly directly home, if on its return it encounters an obstacle as I believe happened in your case, your craft will stop then climb to clear obstacle I’m not certain as I don’t have manual handy but I think 15 m above obstacle, it will then continue to homepoint, it has know upward sensors so cannot see balcony above it .
I think what may have happened in your situation is MPP stopped for Obstacle it then proceeded to climb but most likely crashed into balcony while climbing to clear obstacle, I have seen this happen a few times with original mavics particularly with trees, since those original mavics dji has changed failsafe Rth procedure , for instance spark will stop at obstacle then back up 15 metres before climbing to avoid obstacles and with mavic air and M2 they operate a retrace procedure.

Ohh!  That's a good thought.  Maybe it did stop, but  "the climb"  did it in.  
I'm going to try to learn about looking at the flight log, and seeing if I can learn anything from that.
Might take me a few days to figure it out.  Thanks.  
9-12 17:05
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UPTGrad
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Ohhh!  Dummy me.  I think I understand the situation a little better.
If anyone is interested, I’ll share my sad tale so maybe someone else can avoid the same rookie mistake.
I was flying recreational nearby an airport.  I wanted to follow the LAANC altitude limits as listed in Airmap.
My first approved flight was near the 200 ft altitude limit, so that’s what I ask for, and got approval.
I wanted to be extra careful, so I set the settings “Set Max Flight Altitude” to 50 m.  (~ 164 ft).
This is fine for the area.  No problem.
My next few flights were literally just a few feet to the south, where the altitude limits change to 400 ft.
I got approval via Airmap for up to 400 ft.
Well, I reviewed the Flight log on my iPad.   Since I lost connection, I didn’t think I would find anything useful there.   But… it showed a message as it started its RTH.
“Max Flight Altitude Reached.  Adjust in Main Controller Settings if necessary”

So.  I forgot to change the Max Altitude limits  back to 400 ft.  Had I done so, the MPP would have been able to fly above the building during RTH.  At this point, I don't think the MPP has any logic to fly around the building to regain connection.
I have never really adjusting this setting in the past because I usually fly in areas where AirMap approval is not necessary.  Sad, but I have “Max Altitude – Check” right there on my checklist.  Just hardly ever used.   
So, I think I am a little surprised at how fast one can lose signal behind a building or trees, even if close.
Anyway, lesson learned for me.

[Edit]  Since Airmap's altitude blocks are 200 & 400 ft, but the DJI altitude input limits are in Meters, I have now added "60m" / "120m" to my checklist as a reminder what these values are.

9-15 21:34
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