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Cell phones and other electronic devices can interfere with the pilot's comms and other crucial avionics, as well as cell towers on the ground, if the plane is low enough. Due to these issues, the FCC forbids using cell phones on planes, while the FAA allows airlines to choose when they may be used, once the plane is out of range of the ground cell towers.Source

The fact is, though, many people just don't put their phones on airplane mode. You can forbid it all you want, but without enforcing it (not feasible - too many ways to get around it), it doesn't do much.

Enter the Faraday cage.

Faraday shields are, in short, metallic surfaces that prevent the transfer of electromagnetic waves from one side to the other; Faraday cages are ones with holes in them, blocking waves of specific wavelengths while allowing all others through. You've surely seen Faraday cages before; they're in the doors of all microwaves.

This seems to be an easy (perhaps somewhat expensive) solution. Just put one up on every airplane, maybe with a wire going from one side to the other to allow the on-board Wi-Fi to still work. But it would block all outside communication, regardless of if you've got airplane mode turned on or not. If the cage is routed around/inside the sides of the planes and across the door between the cockpit and the cabin, the pilot would have no problem communicating with the outside world.

I feel like I'm overlooking something obvious, but I can't put my finger on it. Is there a hole (so to speak) in this theory?

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  • $\begingroup$ Cross-posted from Travel.SE. $\endgroup$ – DonielF Oct 2 '17 at 20:24
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    $\begingroup$ An airplane cabin already has something like a Faraday cage around it: the fuselage skin. I wonder if radio interference from electronics is blocked by the skin and thus escapes through the windows? Making the cabin into a full Faraday cage would probably mean putting wire mesh over all the windows. $\endgroup$ – Terran Swett Oct 2 '17 at 20:36
  • $\begingroup$ @mins I’m not sure I understand. $\endgroup$ – DonielF Oct 2 '17 at 20:46
  • $\begingroup$ @Sanchises Not necessarily. Treated glass can be a Faraday shield - see the pictures in the linked Wikipedia article. $\endgroup$ – DonielF Oct 2 '17 at 20:47
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    $\begingroup$ Welcome to aviation.SE! I think @mins means, why would you want a Faraday cage in an aircraft in the first place? We have a lot of "why don't..." questions on this site, and the answer is inevitably some variation on "too heavy/expensive/inconvenient compared to the benefit". We've already established that using phones on board is not a serious aviation issue (at least in the US), so it isn't clear what problem you think this would solve. $\endgroup$ – Pondlife Oct 2 '17 at 21:19
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Cell phones and other electronic devices can interfere with the pilot's comms and other crucial avionics

As far as I can tell, nobody ever demonstrated an actual case of this. At least as long as the electronic device is FCC compliant, but all the consumer electronics has to be.

Keep in mind that all the avionic systems already have to be shielded against interference originating outside the aircraft and this shielding works for that in the cabin too.

Due to these issues, the FCC forbids using cell phones on planes

No. It is due to the issues with the network. Moving mobile clients introduce frequency shifts due to Doppler effect and timing shifts. The system is only designed to handle them for the speeds of cars, but not much higher, so mobile client in an aircraft will not only have unreliable connection, but will also cause problems for the other clients on the ground.

In part, it is also so they don't have to explain everybody over and over why the batteries drain so quickly.

FAA allows airlines to choose when they may be used, once the plane is out of range of the ground cell towers.

The aircraft is never out of range of ground cell towers, since the range is 35 km and the cruise altitude is only 10–12 km.

FAA allows airlines to choose when they may be used as long as appropriate relay is provided so they actually do work.

without enforcing it, it doesn't do much.

As long as only effect ever actually observed is that that phone's battery quickly drains and the phone turns off anyway, nobody cares anyway.

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  • $\begingroup$ @mins, yes. FAA and EASA both allow (see this related answer) airlines to install a cell that forwards calls via sat link and then cell phones may be used on board. Not sure how many actually do it; it's not that common in practice. However, the same rule permits installing WiFi servers and that is quite common now. $\endgroup$ – Jan Hudec Oct 2 '17 at 21:37
  • $\begingroup$ @mins, the phone also probably would work as is, but the connection would be somewhat unreliable and the battery would be draining quickly. The main reason it is forbidden is the associated load on the ground network. $\endgroup$ – Jan Hudec Oct 2 '17 at 21:39
  • $\begingroup$ @mins, yes, that's the case that is permitted. If the plane has its own cell, you may use it (subject to horrendous roaming charges, of course). $\endgroup$ – Jan Hudec Oct 2 '17 at 21:40
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    $\begingroup$ Afaik, the network problems are no longer a concern with newer wireless systems. The FCC was all prepared to lift the ban and the airlines managed to get them to continue it. I believe the airlines are citing safety concerns, but passengers are also against it. They don't want to listen to people on the phone the entire flight. $\endgroup$ – TomMcW Oct 3 '17 at 4:33
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    $\begingroup$ It is quite common to hear the interference from the cell phone on the sound amplifier present nearby. If there is a possibility that this "Bu-bubu-bububu" will interrupt a critical message inside the cockpit, I understand why not allowed. $\endgroup$ – h22 Oct 3 '17 at 6:30
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A Faraday cage for the entire aircraft is not necessary. All the avionics are inside metal enclosures so they have their individual little Faraday cages. Resistance to electromagnetic interference (EMI) is part of the design, affecting not only the enclosure but the design process of the electronics themselves.

Airbus A320 avionics

Cabling can be designed with a shield (foil or braided wire around the signal cabling), or it can be designed to reject interference (balanced signalling).

Installing a Faraday cage to isolate the passenger cabin from the avionics would only eliminate one possible noise source. Modern aircraft are full of electric systems, and each of them is a potential source of noise. So aircraft electronics have to be shielded not just from passenger phones, but from each other.

Aircraft electronics have to deal with strong sources of EMI: radar and lightning.

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