Depending on the phone model and OS, airplane mode may disable Wi-Fi and Bluetooth, but it won't turn off GPS. If the iPhone is one of those devices, it could

Depending on the phone model and OS, airplane mode may disable Wi-Fi and Bluetooth, but it won't turn off GPS. If the iPhone is one of those devices, it could detect a fast elevation change and not reboot the phone until it comes back down in elevation in a motionless state.