GPS

Yesterday, in a moment of ennui on the plane back from Milan, I checked Google Maps on my phone to see if I could ascertain where the plane was. I was extremely surprised that my phone's GPS was still running, as I thought Airplane Mode switched of all TX and RX activity; however, GPS still remains active.

Obviously, given your phone GPS assumes you're at ground level, there is a slight error, with the GPS putting you slightly behind your actual location - as noted when flying over the French coastline, but this disappears as you come in to land.