Aircraft behavior for simultaneous lost link and gps signal loss?

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Hi all,

I operate a Phantom 3 Pro and I am looking for information on the expected aircraft behavior in a situation where the aircraft loses both comm link with the controller and gps signal (or gps becomes inoperative) at the same time.

Based on the forum thread references below, my understanding is that in this "flyaway" scenario, the aircraft will drift with the wind and eventually autoland when the batteries get sufficiently low (as opposed to autolanding immediately)

Can anyone confirm this expected behavior? Has anyone tested this or have experience with this scenario?

Thank you,

Keith

Forum Discussion References:

P2V Lost signal, lost visual what happens next?

"Well, if you have no GPS.. it would be in ATTI mode and drift with the wind.. until the battery ran low and autoland kicked in."

What happened
 

msinger

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I am looking for information on the expected aircraft behavior in a situation where the aircraft loses both comm link with the controller and gps signal (or gps becomes inoperative) at the same time
Using the default settings in DJI GO, the Phantom would auto land at its current location.
 
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Thank you for the quick response.

OK so I now understand that the expected behavior is for aircraft to autoland immediately at its currently location if it loses both comm link and gps signal.

This is good to know as I am trying to address risk mitigation for a "flyaway" in my request for an FAA certificate of waiver to operate in Bravo airspace.
 

msinger

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If you'd like to learn more, you can download the P3P manual here.
 

alokbhargava

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Please check your Rc Signal lost condition is set to "Landing" or to "Hover" if thats your need.In "landing" setting, aircraft will land at the same place after continued signal loss whereas in "Hover" setting, it will land when batteries goes down. In most of the cases, "Hover" is a better option as you get time to plan your next actions.

GPS signal is used to control the position and return to home. If thats not available, which is vey unlikely, your aircraft will start drifting until you take control by moving to ATTI mode. If you lose control signal too, then it will behave as per the signal lost settings described above.
 
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Interesting....OK so depending on the DJI GO settings, there are two possible aircraft behaviors when it loses both control signal ("lost link") and GPS signal simultaneously:

A. Immediate autoland at the aircraft's current location ("Landing" setting -- the default)

B. Hover and eventual autoland ("Hover" setting")

Unless mistaken, I see two possible outcomes with "Hover":

1. Aircraft maintains position over the ground via its Vision Positioning System (assumes VPS requirements are met such altitude and surface texture/patterns)

2. Aircraft "flyaway" as it drifts with the wind.

In both 1 & 2, aircraft should maintain altitude via built-in barometer.

I agree that simultaneous loss of controller signal and GPS signal seems unlikely. However, my proposed operating area is a resort swimming pool surrounded by tall hotel towers in an urban downtown area. Frequency interference from the hotel's computer wireless networks are also a concern.

Unless I missed something, I don't believe the user manual mentions this specific scenario -- simultaneous lost link and GPS signal loss. Maybe because it's not likely to occur and it's a little scary -- like behavior B.2. above!

Thank you.....
 

Meta4

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I agree that simultaneous loss of controller signal and GPS signal seems unlikely.
Unless I missed something, I don't believe the user manual mentions this specific scenario -- simultaneous lost link and GPS signal loss. Maybe because it's not likely to occur and it's a little scary
What is going to cause loss of GPS?
GPS is very reliable and doesn't just drop out
Trying to think of a scenario that would cause a loss of GPS I can only think of:
GPS hardware malfunction - extremely rare
You fly under cover or in a canyon that blocks out your sky view and satellites - depends on where you fly
You screw up the compass by calibrating on top of steel or reinforced concrete which forces the Phantom to default to atti mode​
Since your hypothetical involves losing signal as well, you'd have to consider how likely that is too based on experience flying at your location.

In three years flying I've never lost GPS and I've only ever lost signal because I've flown too far or into a dead spot where an obstacle blocks signal.
 
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alokbhargava

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If you are surrounded by tall buildings, you may see message Non GPS mode (VPS) or ATTI mode, you got to pick one and use it. I would suggest you to fly in ATTI mode and use VPS if you are flying low. Problem with VPS is that if you are flying very low, it keeps on adjusting altitudes for sudden variations such as for a raised platform etc. One should try to practice in such surroundings.

If you are flying high, barometer will take care of height stability but lateral stability will be affected as you don't get GPS and thus you need to go for ATTI mode where you can control positions manually and GPS will not play any role. But are you sure you are seeing GPS issues?
 
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Thanks for sharing. Perhaps an academic overkill exercise, but I am really just thinking worse case scenario here for the purposes of a waiver to operate in a somewhat challenging urban canyon environment in controlled airspace.

I am looking to operate over a pool area (about 200x200 ft) surrounded by 40-story hotel towers on all sides (and in Class B airspace near a major airport). Will be doing GPS interference testing at the ground level to get some data points. I am used to operating in wide open areas so this is new to me and perhaps I am overthinking the risks.

In my waiver request, I figure the FAA might wonder whether I have considered this scenario (combo loss of gps and comm link), my plans to mitigate the risk, and how the aircraft is going to respond.

Thank you all for your help. It now seems a "flyaway" is highly unlikely. Crossing fingers that my waiver application will be approved.
 

alokbhargava

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Thanks for sharing. Perhaps an academic overkill exercise, but I am really just thinking worse case scenario here for the purposes of a waiver to operate in a somewhat challenging urban canyon environment in controlled airspace.

I am looking to operate over a pool area (about 200x200 ft) surrounded by 40-story hotel towers on all sides (and in Class B airspace near a major airport). Will be doing GPS interference testing at the ground level to get some data points. I am used to operating in wide open areas so this is new to me and perhaps I am overthinking the risks.

In my waiver request, I figure the FAA might wonder whether I have considered this scenario (combo loss of gps and comm link), my plans to mitigate the risk, and how the aircraft is going to respond.

Thank you all for your help. It now seems a "flyaway" is highly unlikely. Crossing fingers that my waiver application will be approved.
All the best!
 

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