Flight Mode
(Airplane Mode)
AKA "offline", "radios off", or "standalone" mode
Some phones and other wireless devices have a special "flight" or "airplane" mode that turns off just the wireless radio parts of the device, for safe use on an airplane where some or all radio transmitters are not allowed.
Most airlines and many governments ban the use of cellular radio devices during flight. The main reason for this is to prevent any potential interference with the plane's onboard systems that could affect safety. But also, a phone active on the network (even when idle) at such high elevations and high speeds is taxing on the phone and the network. It will work only intermittently, can degrade network performance, and drains the phone's battery quickly.
Airplane mode therefore allows the user to safely use the non-cellular functions of a phone on an airplane during flight.
The most powerful radio in a phone is the typically the cellular radio, which is why it is a concern for interfering with a plane's systems. But other radios found in most phones — such as Wi-Fi and Bluetooth radios — operate as much lower power levels and have much shorter ranges. These radios are therefore not banned during flight and can be activated even while in flight mode on most phones.