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According to Verizon (a large company generally positioned to be a trusted source of knowledge for how cellular phones and cellular networks work):

When using Wi-Fi Calling, 911 calls will always try cellular service in the local market first, even when the device is in Airplane Mode or cellular service is off. If cellular service isn't available and the user has set up Wi-Fi Calling, the 911 call will route using the registered address.

If a cell phone is in Airplane Mode with cellular service disabled, how can it connect to cellular service in the local market? Under what other conditions might cellular transmissions happen despite the user's efforts to disable cellular transmission capabilities?

Consistent with the explanation of cell phone user interfaces (which should be an authoritative source about what the feature does), similarly positioned wireless network provider SaskTel explains, unqualified (as far as cellular service is concerned), that

Most wireless phones and devices have a setting that allows you to turn off all network connections. This might be called "Airplane Mode," "Flight Mode," or there might be an option to "turn off all connections." When this mode is on, your phone can't make or receive calls or text messages, or access data services such as email or the Internet.

The conflict between these claims is central to the present question.

It could be useful to know what conditions override settings for Airplane Mode and cellular service, both for concerns one might get after reading a lot from Edward Snowden or news about SCIF-storming and/or thinking about potential impact of intentional transmitters on commercial aviation. (I assume that for example, accurate perceptions of strong emergency situations aboard commercial passenger aircraft are likely to be highly correlated among a relatively large number of passengers; it would be unfortunate if that led the emergency to be exacerbated contrary to clear UI labeling.)

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    My reading is that on recognizing a 911 call, the phone itself will temporarily re-enable cellular capability regardless of user settings. – Andrew Lazarus Nov 14 at 21:37
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    @AndrewLazarus Yes, exactly. That's my understanding of it, too. It just turns on the cellular radio and tries to use it even though it's set to off. – reirab Nov 14 at 23:32
  • The wikepedia page on Airplane Mode mentions that some phones allow it and others don't. No citation there though so it can't be an answer. – Jerome Viveiros Nov 15 at 10:16
  • Note that on modern mobile phones 112 (emergency telephone number) - Wikipedia works almost everywhere in the world, without one's needing to know local emergency numbers. E.g. 911 in North America, 999 in Britain, 000 in Australia. We should all learn to use that number instead, especially when traveling. – Ray Butterworth Nov 15 at 14:11
  • You have extended the question far beyond the claim. – Oddthinking Nov 15 at 17:05
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Airplane mode is software controlled. In other words, when you touch the screen in the area that indicates "activate airplane mode" the software behind the scenes changes some data that prevents calls being made.

Nothing fundamentally prevents other software from turning the radio back on. For example the phone app might re-enable the cellular connection when it detects a 911 call is being made. It's just a case of permissions and how the software interacts with apps and other pieces of software. So if some other software (such as the built-in phone app) detects that a call needs to be made, and the operating system gives it permission, the other software can re-enable the cellular connection.

EDIT

The facts that I state above are pretty fundamental to software development, and anybody who has worked on this sort of software (as I have extensively), or probably any sort of software, will understand. However since there are probably people who haven't worked on phone software here are some references:

  • This question talks about how apps can disable or enable airplane mode, and while it doesn't work on all OS, it proves that there is nothing technically impossible about doing it.
  • The settings app can disable airplane mode. Fundamentally the settings app is just an app, with special permissions. If the settings app can disable airplane mode, then other apps with the same permission can also do it.
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    That is only half an answer (and has no source). The important question is of course which software is allowed to deactivate the Airplane Mode. A normal app for example should not be able to do it. – FooTheBar Nov 15 at 15:22
  • Airplane mode disables the cellular radio. You can't just "ignore" having no connection. – TheWanderer Nov 15 at 16:02
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    @TheWanderer You misunderstand my point. Airplane mode disables the cellular radio, but other software can turn it back on again. – DJClayworth Nov 15 at 16:12
  • @FooTheBar Exactly. That's what I mean when i say " It's just a case of permissions and how the software interacts with other parts." – DJClayworth Nov 15 at 16:14
  • I am not even sure if airplane mode disables the cellular radio interface completely, or if it just disables transmission? If the cellular radio system is still receiving and aware of available networks in the area, it will immediately and with no delay be able to re-enable transmission and make an emergency call if requested to do so. – Tor-Einar Jarnbjo Nov 19 at 7:21

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