GPS Signal lost, Switched to ATTI Mode, Flew the drone home

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#1
I flew my drone in the coast and tried to take some photo of a small island. It is only about 300m direct distance from home point, and about 3500m to a military NFZ (see the figure in red square, blue is military NFZ). Drone was taken off smoothly with GPS level about 14. I started to fly to the small island with altitude about 110m in P mode. Before the drone reached to center of the island, all GPS signal suddenly lost. The compass was abnormal and IMU abnormal. The drone switched to ATTI Mode, RTH function disabled. The drone floated within 8miles/h wind and flew far and far. The battery level was about 85%.

I was a little bit panic, but fortunately I trained myself how to fly with ATTI Mode, I found out the orientation and so I can enter the correct stick commands to offset the drift from the wind. After struggle for about 8 minutes, I pulled the drone back to the home point safely. During the way home, the RC didn’t gain any GPS, and still showed compass error and IMU error. After I came back to home, I re-calibrate all.


What I learned are:

1. Training yourself with ATTI Mode until you can control the drone smoothly with 5-10 miles per hour wind;

2. Do not panic, and find correct stick commands, then controlling the drone becomes easy;

3. Nerve try to fly 5 miles near NFZ.

4. Do not fly drone over a big bridge (I flew my drone and took photos over a key bridge and an overpass, and lost GPS signal. I flew back in ATTI Mode too).
 

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#2
Has happened to me too! Good advice, practice in Atti, don’t panic and watch where you fly! Glad it all worked out for you.
 
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#4
Has happened to me too! Good advice, practice in Atti, don’t panic and watch where you fly! Glad it all worked out for you.
Thank you for your reply.

Learning how to control the drone in ATTI Mode is the only way to save your drone when GSP/Compass/IMU are totally abnormal.
 
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#5
Thank you for your reply.

Learning how to control the drone in ATTI Mode is the only way to save your drone when GSP/Compass/IMU are totally abnormal.
Sooo true! I’ve had to do this on my Inspire 2 It is nerve racking LOL
 
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#6
Yes, great advice! Actually I've been intending to beef up my ATTI flying skills and your story just gave me a ton of incentive.
Find an open space, you can practice ATTI Mode fly. Start from 4-5m (no obstacle around). Try both sides toward you, and front drone toward you and back drone toward you. Then gradually rise your drone, until 100m, until 8-10 miles/h wind. It is easy, coz you can switch to GPS mode anytime. After you become skillful, you can easily control the drone.
 

Meta4

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#10
I flew my drone in the coast and tried to take some photo of a small island. It is only about 300m direct distance from home point, and about 3500m to a military NFZ (see the figure in red square, blue is military NFZ). Drone was taken off smoothly with GPS level about 14. I started to fly to the small island with altitude about 110m in P mode. Before the drone reached to center of the island, all GPS signal suddenly lost. The compass was abnormal and IMU abnormal. The drone switched to ATTI Mode, RTH function disabled.
Have you identified the cause of the compass error that forced your Phantom into atti mode?
 

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#15
Yes, it was the exact situation I met. RC also showed that I needed to calibrate GPS and IMU.
Calibrate GPS? There's no way to do that.
If you mean that you think the app was telling you to calibrate the compass, the actual situation was most likely:
Your compass was telling you that you were attempting to launch from too close to something steel.
The actual message it would have given would be .. Magnetic Field Interference Move aircraft or calibrate compass.

DJI's wording is bad and the proper action is almost always to move the drone away from the source of the magnetic interference - not to recalibrate the compass.
Was your launch point a reinforced concrete surface?
4. Do not fly drone over a big bridge (I flew my drone and took photos over a key bridge and an overpass, and lost GPS signal. I flew back in ATTI Mode too).
Flying over a big bridge would not cause any issues unless you fly closer than 10-12 feet and if you did, flying higher would fix that.
 
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#16
Calibrate GPS? There's no way to do that.
If you mean that you think the app was telling you to calibrate the compass, the actual situation was most likely:
Your compass was telling you that you were attempting to launch from too close to something steel.
The actual message it would have given would be .. Magnetic Field Interference Move aircraft or calibrate compass.

DJI's wording is bad and the proper action is almost always to move the drone away from the source of the magnetic interference - not to recalibrate the compass.
Was your launch point a reinforced concrete surface?

Flying over a big bridge would not cause any issues unless you fly closer than 10-12 feet and if you did, flying higher would fix that.

There was no big concrete surface, but only about 80cm footpath right along the beach side. In addition, there was no GPS problem when the drone was taken off. All error information, GSP lost, recalibrate, switching to ATTI, happened on the way to the small island.



I don't know whether the watchtower matters?
 

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Meta4

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#17
There was no big concrete surface, but only about 80cm footpath right along the beach side. In addition, there was no GPS problem when the drone was taken off. All error information, GSP lost, recalibrate, switching to ATTI, happened on the way to the small island.
Are you saying that you took off from a concrete footpath?
If so, it probably had steel reinforcing and is probably the cause of the issue.
I don't know whether the watchtower matters?
It's unlikely that a watchtower had any effect.
Your flight data will probably make things a lot clearer.
To check your flight data, go to DJI Flight Log Viewer
You will find instructions there to upload your flight record from your phone or tablet.
You can post a link to the report it shows you and others might be able to work out what happened.
 
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#18
There is still an unanswered question: In ATTI do you still have an orientation mark at low left corner or not ?!
 

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#19
There is still an unanswered question: In ATTI do you still have an orientation mark at low left corner or not ?!
It should. Atti mode doesn't do anything to stop the compass from functioning.
 
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#20
There is still an unanswered question: In ATTI do you still have an orientation mark at low left corner or not ?!
Straight out of the manual....... A-mode: when neither the GPS nor the Vision System is available, the aircraft will only use its barometer for positioning to control altitude. The Vision System and some advanced features are disabled. Therefore, the aircraft cannot position or auto-brake and is easily affected by its surroundings which may result in horizontal shifting. There is nothing to say any other systems are affected.

In my experience, flying in ATTI mode means the controls are more sensitive and you need to brake yourself rather than relying on position system braking. The aircraft will drift with the wind unless you control it.

Regardless of which mode you fly, if you lose VLOS, you should always be able to use the flight telemetry to bring the aircraft home. Just make sure that you have enough altitude so as not to collide with tall objects.
 

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