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According to

http://support.apple.com/kb/ht1355

airplane-mode on the iPhone shuts off Wi-Fi, Bluetooth, ...GPS.

My understanding is that GPS-devices only /receive/ GPS signals, they don't transmit anything, so I don't understand why this needs to be shut down. [Of course, if the iPhone is running at all, then /it/ is emitting some RF, but I don't see why receiving GPS signals should cause an additional problem for the airplane.]

I tested on an iPhone 3GS (IOS 6.1.3): Enabled airplane-mode, then turned-off the phone. Rotated the phone 180-degrees. Turned it back on (with airplane-mode still enabled). The compass-app still seemed to find North.

Would someone be willing to do an independent test of this?

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4 Answers 4

Yes, airplane mode shuts down the radios that amplify all antenna circuitry. Compass isn't affected by airplane mode other than not being tuned by GPS location. Your observed relative changes will be mostly unaffected but absolute accuracy could suffer between one and ten degrees on much of the globe.

Of course the GPS signals still hit the iPhone case and antennas, just the hardware doesn't do the work to fix a location from those signals while in airplane mode. (Nor does e software do any processing of the location updates which is a big part of the functionality for many people as opposed to the hardware side of the radios being idle / off / silent)

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Ta; I didn't realize the 3GS has a Magnetometer chip; IIUC, the 3G did not. Is it fair to say the following?: There is no conceptual reason for GPS to be shut-down in airplane-mode. Then, while flying cross-country, you could see your longitude, latitude (tho' you wouldn't have maps, unless downloaded before the flight) and altitude without emitting any more RF that simply by having the iPhone powered-up. But there might be a cost-savings reason, if it would make the chip-set more expensive to have the capability of shutting down part of it?? –  gentsquash Aug 12 '13 at 2:41
    
→ gentsquash: you already correctly tested it. "Yes Compass isn't affected by airplane mode". –  daniel Azuelos Aug 12 '13 at 6:20
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→ gentsquash: you are right, there is no technical reason to shutdown a GPS chipset which is just a receiver and antenna, since the emitter will not be shutdown. The emitter is a flock of satellites and their 1.575 GHz is sprayed on the whole earth through every airplane, through every vehicle, through every human being. –  daniel Azuelos Aug 12 '13 at 6:36
    
The local oscillator of radio receivers emit a small amount of RF. Even though the tiny amount emitted by a current GPS is not likely to interfere with anything, that was the technical reason due to cheap old radios from decades ago. –  hotpaw2 Aug 13 '13 at 0:37

I think Airplane Mode disables the hardware chips. GPS and 3G/LTE are on the same chip. I would say, Airplane Mode also disables GPS.

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Yes it does. Location service isn't accessible on Airplane Mode. –  Matthieu Riegler Aug 11 '13 at 22:21
    
Does it also disable the compass on your iPhone? [Location service might need additional information, e.g, a cell-tower or a map.] –  gentsquash Aug 11 '13 at 22:30

The compass uses the Magnetometer/Gyroscope which doesn't require antennas (just a chip). So yes it still works in airplane mode.

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Yes, airplane mode disables GPS

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