Exactly, turning off Data does not turn off the Cellular chip. Turning On Airplane mode turns everything off. You can then selectively turn Wifi and Bluetooth back on if you need it.
Turning Off Cellular Data will continue to drain the battery regularly while cellular looks for a signal which is what the OP wanted to avoid.
Dr. Kane wrote:
PHil is wrong, obviously gps is hardware, but airplane mode doesn't have levers and gears to disable individual parts, or everything together, each transmitter can be shut off individually, (and receiver) iPhone 5s with iOS 7 had a bug where Ina or plane mode through compass app the gps will re-enable, but wil take a while to lock because AGPS isn't available, iOS8 fixed this I believe. iPad with sim card has GPS as well, disabling data doesn't put the iPad into the airplane mode, thus gps still works, apple likes to shut off gps when airplane mode is on, so it shouldn't work in that mode, for iPhones it's different, disconnecting internet the phone will still waste energy looking for towers and will still get assisted gps.
No, Airplane mode turns everything off. You can then selectively turn Wifi and Bluetooth back on because they are separate chips. i.e it can cut the power to specific chips. Not parts of the same chip.
If you turn off the Cellular hardware, the GPS potion being part of it, turns off also, and you can only turn it on when you turn off Airplane mode, so the entire chip can turn on.
The Compass on an iPhone does not use GPS. It uses the accelerometer much like magentic compass would. The only reason it uses GPS is to show your location, but not your heading. As such the Compass still shows heading while in Airplane mode on iOS 8, but not location.