In my experience GPS locks on planes can be hard especially if your phone's aGPS data hasn't been refreshed recently. IF you just got a clear ground lock before take-off, you should be able to establish a lock mid-air reasonably easily. If that doesn't happen, hold it to the window for a good 5-10 minutes. On B737s and A320s I've had no issues.
On 787s... that's a totally different story. Cell signals struggle with 787s whether I'm in Japan, China or the US. I haven't tried GPS independently because by the time I think about it I remember how I should refresh my aGPS by opening GPS Status but by then I lack network connectivity. But then again I mostly fly on J for 787 routes so usually I'll just enjoy my PDB or just start playing some music to cure my boredom rather than worry about GPS.
Originally Posted by
TGarza
iPhones since I believe the 4S have not needed a data or wifi connection for the GPS to work. A connection is needed for the online versions of Google maps. I have used offline maps without a cell connection on both Android and iOS devices. The Android backcountry map app is one reason I keep my old Samsung which has no cell service.
Fairly certain no phone actually needs a cellular network to lock. The GPS has always been independent of network, but the assisted portion may help download GPS data for a faster lock. The problem with many older phones, especially back when Google Maps didn't have an offline option was they just wouldn't load the map, but a standalone GPS app like Android phones have had would be able to confirm you have a GPS lock and display coordinates.