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Comment by Jayschwa | Hacker News Reader

Devices are supposed to be shut off / put in airplane mode to prevent interference with avionics. Intentionally jamming a part of the spectrum would be counter-productive.

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It's got nothing to do with avionics. It's to stop interference with base stations on the ground.

https://www.law.cornell.edu/cfr/text/14/121.306

No, it's not. All electronic devices are banned by default, "[unless] the part 119 certificate holder [the air carrier] has determined will not cause interference with the navigation or communication system of the aircraft on which it is to be used."

The throwaway is probably thinking of the ban on cell phones, which is an FCC restriction, not an FAA one.

This is correct as this article was concerned around the Samsung phone.

But you're allowed to have phones on the ground.

Within the airport you are nowhere close enough to an antenna for it to matter.

You know how old gsm phones made a d-d-d d-d-d ddZzz-d now and then when near a playing radio?

That is long enough to completely mangle a control tower message. They let phone on grounded plane because a parked plane is not in critical contact with the tower.

Now, having them off by age/model/features would be extremely complicate, most people won't genuinely know if their model is affected etc. So it's all electronic should be switched off or in airplane mode.

Nice theory, but not true. You're allowed to use your GSM phone the second you land, but there is still plenty of critical communication to be done, like negotiating crossing other active runways while taxiing. 100% of runway incursions happen on the ground!

My understanding is that the concern is not interference with voice radio but interference with the more sensitive analog radionavigation equipment, e.g. VOR and ILS. These both aren't used on the ground and don't work on the ground anyway because of antenna orientation and other issues. VOR and ILS are very old and very simple technologies (at least as radio goes), making it fairly plausible that radio interference in particular bands could skew the ILS needle and cause a badly failed landing approach.

But remember that both GSM and ILS/VOR/DME are licensed radio services, and thus shouldn't interfere. The speakers you hear the TDMA modulation in have a sticker on them that says "This device complies with part 15 of the FCC Rules. Operation is subject to the following two conditions: (1) This device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation." Indeed, it does accept the interference that causes undesired operation.

This is a bit of a misinterpretation of Part 15. Part 15 devices bear the "must accept" language to indicate that they enjoy no particular regulatory protection from interference - the operator of a part 15 device may not compel action on the part of another person because that person's lawful operation is interfering with the part 15 device.

Licensed services do enjoy regulatory protection, but that protection doesn't change anything physically - it just means that there is a regulatory remedy when interference is a problem. And one of those remedies is FCC regulations about where other devices can and cannot be used.

While radionavigation equipment should be built to high standards for interference rejection, their being a licensed service is in no way a guarantee that other devices won't cause problematic interference. It just means that when other devices do cause interference, FCC enforcement is a possibility.

around here it is said to keep them off until the plane stops. almost noone does and the pilot aren't screaming at them, so there's that.

That was the original intent, I guess, and it’s better to err on the safe side, but as far as I know, it’s not actually clear that they do interfere. And the FAA doesn’t regulate mobile devices on aircraft, leaving it up to the FCC and individual airlines.

But of course you can’t jam the part of the spectrum you intend to use. :P

Well, if you have a FHSS frequency hopper, you could jam on all the channels except the one you are talking on at that instant (for 50ms or however long you hop). That would make the spectrum unusable by anyone except you. (It's also why regulatory bodies have strict rules on how long (and short) you can idle on a channel, how you have to hop through all channels before transmitting a second time on one, etc...)

The jamming would not be routine--not a substitute for keeping a channel clear--but would be available as an emergency measure if for some reason it became necessary.

Depending on how much of the spectrum is jammed, the pilots might have to fly without some avionic support for a time until the issue is resolved, but they should be able to do this, anyway. If they can't fly on manual, then a passenger with electronics designed to interfere with avionics could crash the plane.

A cheap $50 phone from 2010 can stay constantly connected to 6 base stations (at 6 different frequencies) and swap over between them in milliseconds.

You'll need to emit 100 times the power of a phone over a wide range of frequencies to jam them.

It's not even counter-productive, it is destructive. Don't suggest that as an idea in a plane.

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