8 Replies Latest reply: Nov 14, 2008 11:41 PM by Malcolm Rayfield
MZGruba Level 1 Level 1 (5 points)
I haven't found a post covering this, so I will give it a go here.

Why does the iPhone 3G shut down GPS when in Airplane Mode?

My work is easily disrupted by transmissions from devices like mobile phones, bluetooth, WiFi, etc. So I have always purchased phones with an airplane mode, so I can continue to use the PDA functions of the device, without having the extra radiation issues/interruptions.

Airplane mode is named for its original purpose, to shut down all radient functions of a mobile device while in flight on the somewhat dubious fear that amplified radients from a mobile device could disrupt aircraft electronics, supposedly causing anything navigation inconsistencies to crashing the airplane.

The thing is, GPS is a non-radiant function, it does not transmit data, it listens to and processes data from a navsat constellation overhead. Since it is a non-radient function, why is it disabled in Airplane Mode, which is function specifically design to suppress radient functions in mobile devices?

Are there any Apple people reading these forums who can offer a rational? Because to me, this makes no sense.

MacBook Pro, Mac OS X (10.5.5)
  • neuroanatomist Level 7 Level 7 (31,690 points)
    Airplane Mode shuts down all radios in the iPhone. While it's true that the GPS radio is a receiver only, it's also true that there is not much utility to the GPS without a data connection to download the maps on which your location is plotted. Furthermore, Location Services uses assisted GPS (aGPS), which uses data from assistance server on the cellular network to speed up localization and compensate if too few satellites are in view.

    Granted, the GPS receiver does function without the assistance part, and there are apps that store your path, readout your lat/long/alt, etc.

    So, I suspect part of the rationale is that even though the GPS radio is a receiver and does not transmit, it's functionality is pretty crippled without a data connection, so it might as well be shut off.

    Having said that, although Apple employees read these boards, those that respond do so as volunteers on their own time - you should not expect a technical response from Apple here in these user-to-user forums.

    You can submit feedback to Apple: http://www.apple.com/feedback/iphone.html.
  • HeloCaptain Level 1 Level 1 (10 points)
    After entering Airplane mode, one can activate WiFi, leaving the phone's cellular radio off (yes, the WiFi radio will be on).

    The GPS should work in that environment, though maps will not be downloaded unless there is an accessible WiFi signal available.

    If one downloads (via taps or finger zoom) a map that includes the entire scope of travel anticipated, I suspect (but have not experimented) that the GPS would show one's travel progress, though not in great detail (due to the large map area).

    On my next commercial flight, I plan to load the continental U.S. in G maps and determine if the GPS will track under these circumstances (assuming I can get a window seat so the satellites can be seen by the phone). I'll try G Earth on the return trip.

    \[For pilots reading this, I will not activate the WiFi radio if flight conditions are IMC.]
  • edclange Level 3 Level 3 (900 points)
    I flew to Calgary a month ago. GPS devices were included on the printed and announced list of electronic devices that are forbidden to use in flight. It's quite likely that Apple needs to follow some sort of FAA or FCC rules for what it calls "Airplane Mode." I can't find anything on faa.gov.

    AM/FM radios are also forbidden in flight, even though they do not transmit.

    Your profile does not indicate your location, so I can't say if FAA/FCC rules apply to you. Chances are, all countries with airports have similar airline passenger regulations.
  • icebike Level 3 Level 3 (740 points)
    GPS is a airline specific restriction, not an FAA or CAA restriction. Be that as it may, you still have to obey.
  • icebike Level 3 Level 3 (740 points)
    You can also find several apps in the app store that show you where you are (lat/long) and speed.

    However, even with a good GPS, its hard to get a signal in a plane even with it pressed against a window. The speed contributes to this because the consumer grade chipset is not designed to obtain a fix at those speeds.
  • Malcolm Rayfield Level 7 Level 7 (28,075 points)
    So, I suspect part of the rationale is that even though the GPS radio is a receiver and does not transmit

    Many receivers emit some RF signals from oscillators used to shift the input signal do a lower frequency for processing. Because of this, receivers, as well as transmitters may be banned.
  • icebike Level 3 Level 3 (740 points)
    There are no emmitions from ocilators in a digital single chip radio.
    Your age is showing.

    Gps is not banned by the FAA, only by airlines and perhaps security agencies.
  • Malcolm Rayfield Level 7 Level 7 (28,075 points)
    Just putting everything n one chip doesn't mean a receiver won't emit radiation. There are still high frequency signals there, whether they are local oscillators, or digital clocks.