Hi all,
Terrible day - made 5 good flights on a breezy day and on the 6th flight of the day, I lost control of my almost-new Mavic 2 Pro and it flew off, eventually out of controller range, and is lost.

I took off with GPS lock and had home set and flew within visual range (less than 200 meters) for 2 minutes at 50m altitude.

The terrain I was flying over was just flat farmland (rice fields) and a small river.

All was going fine, and I had 17 satellites and the Mavic 2 was handling the strong breeze just fine (as it had all day)

Then after 2 minutes of strong GPS, I suddenly lost all 17 satellites in an instant, regained some sporadically, then lost them all again.

GPS never regained a lock, so return to home did not work (despite repeated tries)

Wind took the drone far away, I wasn't able to orientate, and eventually lost controller contact (no idea of the final destination)

Log shows:
for first 2 minutes of flight there was strong GPS (16-17 satellites)
for the next 4 minutes it has intermittant GPS signal
final 7 minutes has no GPS signal (0 satellites)

All this at 50-60m altititude over open rice fields.

How is this possible?

Flight map
http://www.phantomhelp.com/logviewer/DMY4AF6P8YST85RGUUF8/

Hi, we do feel sorry for what happened. I understand your aircraft flown away and you wanted to know what happened. For us to help you, I suggest contacting PRODUCT SUPPORT and let us establish what happened during that specific flight. Our flight data analyst will conduct a thorough investigation into this by sending your flight data records. We're here to help you. Thank you.

Thanks Gamora,
I already synced my flight records and emailed support.

I'm interested to know if others have experiences this kind of catastrophic GPS failure.

Sorry for your loss.

Seems there was a problem with altitude calculations rather than the GPS.

While altitude was 15 ft there was a message (Maximum Flight Altitude Reached)!! Later, there was some messages related to same issue.

Anyway, did you search for it at the last coordinates in the flight log? I think it landed there or some meters around.

Ahmed Hussain Posted at 11-24 08:20
Sorry for your loss.

Seems there was a problem with altitude calculations rather than the GPS.

That error message doesn't seem relevant, as the drone reached almost 200ft (the hard ceiling here because it's an airport blue zone).

After the GPS dropped out and I lost orientation, I maxed the drone altitude and let it drift in the wind a while until it got a GPS lock again. Unfortunately it never reacquired GPS for the rest of the flight!

I saw unfamiliar terrain in the video feed and I'm sure it landed several kilometers from the last logged GPS position (which was also out of controller range at that point).

Ahmed Hussain Posted at 11-24 08:20
Sorry for your loss.

Seems there was a problem with altitude calculations rather than the GPS.

Hi,

Message is correct. Flying in OPTI mode without GPS means a max altitude of 15 feet.

cheers
JJB

Hi,

Sorry for your huge loss!.

Had a look at your flightlog ;

1) You started this flight in OPTI mode, 5 satt and 0 gps reception,
2)  after 7 second a max height warning, this because flying in OPTI no GPS
3)  after 7 seconds 14 sats found, but no GPS reception bar (still zero)
4)  at 8s  2 bar reception, at 12s 5 reception and HP set, OPTI change to P-GPS
5) at 1m59s GPS sats and reception both to zero!, back to OPTI mode! this at 40 meter height and 86 meters away from home.

Time to fly the craft back home, but more pitch fwd, heading 165 with heading to home is 010.

In ATTI mode the little compass in the GO app shows the heading of your craft, you can use this to direct drone back home.
6) 2m12 13 sats but zero for the reception, so no gps data is used
7) 2m22 16 sats + 4 reception, GPS mode is back on, distance to home 200 meter with heading 9 degree.
8) drone flys hdg 315, so distance to home decreases to 170 meter
9) 2m31 sats dropping from low again, back to zero (same for reception), so back to OPTI
10) heading change by you, looks like it was heading to home in the beginning, hdg to 145 > 220 > 310 so away from home
11) 6m21 OPTI to ATTI
12) 8m55 connection loss, AC starts autloanding

Hard to tell where it landed, because no GPS data that time.

What went wrong?
1) Don`t know why your drone lost GPS signal and why it was hard to get it at the first place.
2) The moment it went in OPTI you could have fly the drone back home, using the compass.

cheers
JJB

JJBspark Posted at 11-24 09:53
Hi,

Sorry for your huge loss!.

I was playing this scenario in my head trying to figure out what I would do if this situation had happened to me.  I've learned a LOT from many of your flight analysis I've seen here including this one.  Very informative stuff........thanks!

JJBspark Posted at 11-24 09:53
Hi,

Sorry for your huge loss!.

Thanks for your really helpful analysis! You are right, I should have flown back home immediately upon GPS loss, but I assumed it was a transient thing and I waited for GPS lock again. Unfortunately I was never able to get GPS back for the rest of the flight.

The autoland I reversed with upstick because it was descending into what appeared to be rice paddies and I had plenty of battery left to get back home (and I still assumed GPS would come back online at some point).

Sato Zoom 2 Posted at 11-24 10:10
I was playing this scenario in my head trying to figure out what I would do if this situation had happened to me.  I've learned a LOT from many of your flight analysis I've seen here including this one.  Very informative stuff........thanks!

Hi Sato,

Practise to fly back using that compass in the Go app.

So if OPTI or ATTI is there (and enough free space around your drone), release all sticks, gain height if needed and YAW craft back to home heading, followed by pitch fwd. (sport if more speed needed).

cheers
JJB

Never let the drone out of your sight. Too many lose them due to not having VLOS and watching DJI GO 4 app instead. I'm sure everyone knows this RIGHT?

rolling56 Posted at 11-24 12:04
Never let the drone out of your sight. Too many lose them due to not having VLOS and watching DJI GO 4 app instead. I'm sure everyone knows this RIGHT?

Yeah, we all know this......

Sato Zoom 2 Posted at 11-24 10:10
I was playing this scenario in my head trying to figure out what I would do if this situation had happened to me.  I've learned a LOT from many of your flight analysis I've seen here including this one.  Very informative stuff........thanks!

It would be the advice of all pilot training courses , and all commercial pilots, that once you enter Atti mode to land as soon and as safe as you can, not to fly home, your aircraft should Never take precedent over the safety of people or peoples property, if you land safe which is a much easier manoeuvre than trying to fly home in Atti mode, you can just go and pick up your craft.

This procedure should start before ever you fly, always have at least two safe areas you can land if you get into trouble.If this was not part of your risk assessment plan when working commercially you would in a lot of cases not get permission to fly particularly in NFZ were SOP is needed to fly.

BTW don’t heed ANDY Pandy he’s just trying to get free easy points from the thread.

rolling56 Posted at 11-24 12:04
Never let the drone out of your sight. Too many lose them due to not having VLOS and watching DJI GO 4 app instead. I'm sure everyone knows this RIGHT?

100% my friend

JJBspark Posted at 11-24 12:29
Yeah, we all know this......

.

JJBspark Posted at 11-24 09:53
Hi,

Sorry for your huge loss!.

This is very impressive JJB - great advice. All the OP really needs to know I'd say. Good work mate.

JJBspark Posted at 11-24 11:19
Hi Sato,

Practise to fly back using that compass in the Go app.

What is OPTI mode?   All I see is one reference in the manual and it only lists the mode - nothing about it.

ff22 Posted at 11-24 13:23
What is OPTI mode?   All I see is one reference in the manual and it only lists the mode - nothing about it.

Opti is optical vision mode it gives you lock from the ground up to a certain height depending on which aircraft you are flying.
Your aircraft has basically 3 flying modes GPS,OPTI, & ATTI, If you lose GPS mode your aircraft will enter next available mode if it is in height range it will be OPTI mode, if you are within height range of vision sensors this will give your craft hold from ground to bottom of aircraft, if this is out of range then it will enter next available mode which is ATTI mode.
These modes should not be mixed up with sport/Tripod which are on your mode button on M2

You should also have  not started the flight in Opti mode and waited for ac to acquire gps.  always wait for the home point..... in this case I don't think it mattered because GPS never returned so you probably wouldn't have been able to hit return home but you should always in the beginning of a flight wait for homepoint to be established. Unless flying inside then u would be in opti mode and depending on light source atti.

$gambino$ Posted at 11-24 19:35
You should also have  not started the flight in Opti mode and waited for ac to acquire gps.  always wait for the home point..... in this case I don't think it mattered because GPS never returned so you probably wouldn't have been able to hit return home but you should always in the beginning of a flight wait for homepoint to be established. Unless flying inside then u would be in opti mode and depending on light source atti.

Home point was set while hovering at takeoff point in opti. I would not fly anywhere until that actually happened. As you said, it's useless if the drone has no functioning GPS at the time you actually want to return to home.

This is a classic example of why there should be an ATTI mode on all quads so that people can practice  flying without GPS signal.

JJBspark Posted at 11-24 09:53
Hi,

Sorry for your huge loss!.

Greatly appreciate your analysis.  From reading your post, I have one question.

In regards to ATTI mode.  

As I understand it, the craft will enter ATTI mode due to either magnetic interference (thus loss of compass) or Loss of GPS signals.  Most times I read about ATTI mode, it's due to magnetic interference, mainly due to pilot error not checking on take off.  The Mavic controller will show "magnetic interference" on it's display, I have seen this a couple of times while attempting a take off, and had to move.  

In this situation, the loss was of the GPS signal, and the Mavic display I assume and DJIGO4 both would display ATTI mode once the GPS signal was lost.  But since it was the GPS signal was lost, and there was no compass error, it's safe to assume the compass was still working?  

If you lose the compass, the do you also lose the compass direction arrow that is displayed on the small compass screen on the lower left of DJIgo4?  

Thanks
Paul C

Hi Paul,

If there is a internal fight between values (IMU, Compass, GPS), depending of wich values are not "equal", most of the times DJI drones skip the use of other data, but GPS and Compass data is still there and available. (if the problem is ofcourse not bad GPS signals etc)

So magn interference to the AC will not give a loss of Compass and/or GPS but data is simple not used, so craft is set to ATTI mode, but the question is ofcourse if GPS and/or Compass data is OK.

Depending of the values most of the times i think that the compass and gps data is ok, so when in ATTI these values can be used.
So in ATTI mode normally the red arrow on the GoApp compass still works (compass data used from the drone compass) and distance is available too (gps data used).

If the problem ofcourse is due to a really faulty compass than i guess (pretty sure) that the red arrow givesan incorrect indication. My own experience with a Spark is that when ATTI pops up the GPS and Compass data still OK.

What i do always: After takeoff fly 10 meters fwd, if you (device+controller) are in one line with the drone (you see the back of the done) the red arrow is facing to the white mark outerscale compass GoApp. Yaw left and right, if it follows OK than compass OK and safe to fly.

IMU does sense a lot, for my Spark rapid multiple YAW movements can cause an "error", so software kills the use of other data > thus ATTI

Hope my explanation is an answer to your questions.

cheers
JJB

Just to update, DJI analyzed the flight data and informed me that they would replace the lost Mavic 2 under warranty.

Thanks to those who generously gave time and offered helpful advice above.

My takeaway from this is that if you lose GPS when flying in wind, land immediately (if there is suitable landing ground below.)

Don't assume that you will be able to regain GPS inflight. Land first and wait for it to return.

If GPS cannot be reestablished then you will at least have the option of collecting the drone near the last GPS fix, or calmly assessing the risk and taking off / flying home by compass in ATTI mode.

paul2660 Posted at 11-25 15:57
Greatly appreciate your analysis.  From reading your post, I have one question.

In regards to ATTI mode.  

Loosing gps on these aircraft is very unlikely, in fact over many years I have seen very few, with magnetic interference you don’t lose gps, your aircraft shuts down gps in favour of compass, the most common cause of magnetic interference is usually picked up from take off area, many things in your envoirment can effect your compass, I will try to explain below what happens when your aircraft is affected by magnetic interference.

The best way I can explain this is. If you put your Aircraft on the ground in normal circumstances, start it up, then lift it up and turn it 90 degrees to the right both your compass heading and IMU will both move together 90 degrees and no problems.
If you put your Aircraft on the ground and there is magnetic interference only the heading of your compass will change, your aircraft will still take off. But when it clears magnetic interference compass will then move to correct heading which you would think was great. But No, what happens is IMU is then conflicted and confused because of this sudden movement by compass, so you receive IMU exceptional heading warning, your aircraft cannot deal with data conflict so decides to switch to Atti mode dropping gps in favour of compass simply because aircraft can fly without gps but not compass.

While I can’t be certain OP picked up interference from the ground or surrounding area it is the most common cause.

paul2660 Posted at 11-25 15:57
Greatly appreciate your analysis.  From reading your post, I have one question.

In regards to ATTI mode.  

This is just a guide.

Compass distances.

Natural and Artificial Magnetic Anomalies Warning
Note
The following information has not been objectively tested to determine it’s impact on a Drones compass accuracy in flight.
        1        Many things can distort the earth’s magnetic field in the area you are flying:
        •        Steel framed or reinforced concrete buildings, bridges and roadways, iron pipes and culverts, high power electric lines, heavy equipment, trucks and automobiles, steel tanks, electric motors and even computers.
        •        Flying between steel framed or reinforced high rise buildings will distort the magnetic field in addition to causing GPS multi-pathing.
        2        Safe distances for compass calibration
        •        6” (15 cm) minimum: Metal rim glasses, pen/pencil, metal watch band, pocket knife, metal zipper/buttons, belt buckle, batteries, binoculars, cell phone, keys, camera, camcorder, survey nails, metal tape measure.
        •        18” (50 cm) minimum: Clipboard, data collector, computer, GPS antenna, 2-way radio, hand gun, hatchet, cell phone case with magnetic closure.
        •        6 ft (2 m) minimum: Bicycle, fire hydrant, road signs, sewer cap or drain, steel pole, ATV, guy wire, magnets, chain-link fence, bar-wire fence, data collectors
that use a magnet to hold the stylus.
        •        15 ft (5 m) minimum: Electrical box, small car/truck, powerline, building with concrete & steel.
        •        30 ft (10 m) minimum: Large truck, metal building, heavy machinery.