Once upon a time, the use of cellphones and wireless devices on an aircraft was strictly forbidden. Now these devices may be used in "Airplane Mode." In an effort to allow users to use functions on their phones that don't require wireless access while in flight, phone manufacturers have developed Airplane Mode to shut down all the phone's wireless capabilities.
Cellphones and Aircraft Navigation
While in flight, an aircraft is in constant radio-wave communication with ground stations via both voice and navigation frequencies. Cellphones operate by transmitting high-frequency radio waves with enough power to reach the nearest cellular tower. In 1991, the Federal Communications Commission banned the use of 800MHz cellphones on aircraft, for fear that they would cause interference with navigation frequencies. Citing a lack of evidence for this, the FCC has proposed withdrawing this ban, but as of the date of publication, it remains in force.
What Airplane Mode Does
Airplane Mode disables both the cellphone and Wi-Fi transponders in the phone. This means that the phone cannot send or receive calls, nor can it contact a cellular network to update the time or other data. It also can not make Wi-Fi connections with other devices, so any applications that depend on Internet connections will no longer function. GPS and Bluetooth functions are also shut off. Airplane Mode is usually accessed in the Settings menu of most smartphones, such as iPhones and Android-compatible phones.
What You Can Do in Airplane Mode
Most smartphones still offer a lot of functionality, even while in Airplane Mode. For instance, applications that don't depend on Wi-Fi access will still function, including games and many productivity programs such as word processors and spreadsheets. Even applications that depend on Internet connections for full function may still let you work in "offline" mode. For instance, your email application may allow you to read email you have downloaded before the flight and compose email to send after you land.
Remaining Airline Restrictions
Federal Aviation Administration regulations still prohibit the operation of any cellphones or portable electronic devices until the plane reaches 10,000 feet in altitude; similarly, these devices must be turned off and stowed during landing. However, a growing number of airlines are allowing use of cellphones immediately upon landing, and some are exploring the idea of providing Wi-Fi services while in flight.