By now, most air travelers are familiar with the routine announcement after boarding: "Please turn off your phone or put it on airplane mode." The question remains whether this is necessary.
The answer is yes, according to the Federal Aviation Administration (FAA). FAA regulations require passengers to switch their phones to airplane mode while flying. As stated on the FAA website, "The FCC [Federal Communications Commission] and FAA ban cell phones for airborne use because its signals could interfere with critical aircraft instruments. Devices must be used in airplane mode or with the cellular connection disabled."
Airlines continue to make this announcement due to concerns that cell signals might interfere with navigation and communication systems. However, evidence supporting this interference is limited. An FAA study from 2012 found almost no instances of cellphone usage disrupting an aircraft.