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You Don’t Need to Use Airplane Mode on Airplanes (gizmodo.com)
submitted 2 years ago by to c/technology@lemmy.world
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[–] 1 point 2 years ago (3 children)

Last time I flew, there was no signal at all while flying. not even GPS!

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  • [–] 2 points 2 years ago (3 children)

    There was GPS signal, it's just by design that chips are not allowed to lock at above certain speed to prevent military use. But even if there's no signal, mobile phone will try to find tower. If it doesn't find one it will try increasing transmission power.

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  • [–] 2 points 2 years ago (1 child)

    But even if there's no signal, mobile phone will try to find tower. If it doesn't find one it will try increasing transmission power.

    Thus draining the phone's battery much faster.

    Same thing happens if you are camping in a remote location with weak or non-existent coverage.

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  • [–] 2 points 2 years ago (2 children)

    That makes sense! Thanks

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  • [–] 2 points 2 years ago (1 child)

    Next time you're on a flight, download a GPS speedometer app and launch it right before takeoff. You'll notice that it'll accurately measure the plane's speed up to around 500 MPH, before it suddenly stops giving you a speed readout.

    Like the other person said, this is to prevent your average dude building a guided missile using an old phone they have lying around.

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  • [–] 1 point 2 years ago (1 child)

    It's a built-in security of the protocol. For accurate speed measurement device would need access to L2 frequencies, which carry encrypted data used for additional corrections, faster calculations, atmospheric conditions, etc. One can certainly get a location tracked through phone, but it's not solely though GPS, it's most likely combination of other positioning systems.

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  • [–] 2 points 2 years ago* (last edited 2 years ago)

    Probably would just use an IMU exactly as the plane itself already does for its own navigation.

    They get a lock on the ground, synchronize the IMU with the Earth's orbit, and they keep track of where they've moved from the origin, supplemented by GPS.

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  • [–] 1 point 2 years ago (1 child)

    What? Every smartphone I can remember owning has gotten a GPS signal if I hold it up to the window. Plenty of planes have GPS on board too. If there is a speed lockout, a 737 isn't enough to break that threshold.

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  • [–] -1 points 2 years ago*

    Speed limit is indeed above speed that 737 can fly (see addendum), but it's not only reason why GPS sometimes doesn't lock. On the plane your phone doesn't get assisted GPS, where rough location calculation is based on ground data like WIFI networks and GSM towers, so time to first fix takes significantly longer because your phone only has access to L1 frequencies. Since it takes a while, 30s for entire satellite message to be transmitted, it's coordinates and the like, and there's no help from ground stations for crude calculation combined with speed of the plane it all ends up contributing to a significantly longer time to first fix or perhaps even problematic fix in the first place.

    So all in all, speed contributes to the problem. Yes signal was present at all times. And no, speed is not the sole factor but contributes a lot. GPS chips have improved quite a bit over the time so some old devices will definitely have a problem finding location on plane. Newer ones won't, especially considering they have access to other networks like Galileo, GLONASS and BeiDou.

    All GPS receivers capable of functioning above 60,000 ft (18 km) above sea level and 1,000 kn (500 m/s; 2,000 km/h; 1,000 mph), or designed or modified for use with unmanned missiles and aircraft, are classified as munitions (weapons)—which means they require State Department export licenses.[126] This rule applies even to otherwise purely civilian units that only receive the L1 frequency and the C/A (Coarse/Acquisition) code.

    Edit: What airplanes have on board, is access to different frequency which your device doesn't. It's not comparable.

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  • [–] 1 point 2 years ago

    Last time I flew, there was no signal at all while flying.

    There's a number of factors that lead to that.

    • The cell base station antennas have a relatively narrow vertical beamwidth and are typically aimed a few degrees below horizontal. (Aircraft tend not to operate at that altitude)

    • usable range of each cell base stations is typically <50 km.

    • Cell base stations are optimized for communicating with mobiles moving less than 90km/h.

    Given all that, if you happen to get a signal, you'll be handing off between towers far too fast and too frequently for the network to reliably deal with.

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