Why do planes require airplane mode?

The requirement has two independent roots. In the United States the Federal Communications Commission, not the aviation authority, has banned the use of cellular telephones on airborne aircraft since 1991. Its concern was the ground network: a phone at 10 km altitude has line of sight to dozens of cell sites at once and would confuse the system that hands calls between towers. The aviation side, the FAA in the United States and EASA in Europe, worries about the aircraft itself. Their rules require operators to establish that portable electronic devices do not interfere with navigation and communication equipment before allowing them in flight.

Every modern aircraft radio and receiver is designed and tested to tolerate radio-frequency noise, and a phone inside a metal fuselage is a weak transmitter. The problem is not one phone but the combination of many, in unknown positions, with unknown faults, transmitting at maximum power because they cannot reach a tower. Instrument landing system receivers, VHF radios and GPS receivers all listen for faint signals, and intermittent noise on those channels is exactly the kind of fault that is hard to reproduce and hard to prove absent. Airplane mode removes the doubt at zero cost. That is why the rule persists even though documented incidents are rare and largely anecdotal.

The picture changed in 2013 and 2014. The FAA concluded that most aircraft could tolerate devices in airplane mode during all phases of flight, ending the old requirement to switch everything off below 10,000 ft. EASA followed and went further in 2014, allowing airlines to permit phones in normal mode throughout the flight if they demonstrate that their specific aircraft type is not affected. Some European operators now do so, and in-flight connectivity systems route calls and data through an onboard picocell and a satellite link, which keeps handset power low and the ground network out of the loop. The 2023 European decision to open 5G frequencies on board rests on the same principle: the aircraft carries its own base station.

For the passenger, airplane mode is a courtesy to a safety culture that prefers to rule out a risk rather than to quantify it. The phone will search endlessly for towers at cruise altitude anyway, draining its battery for nothing, and the airline's Wi-Fi works perfectly well with the cellular radio off.