Do you really need to put your cell on airplane mode while flying?

Airplane mode … Along with fastening your seatbelt and putting your seat in an upright position, flight crews always ask passengers to put their cellphones in airplane mode. But according to a survey, 40% of flyers say they don't do it. Some say they forget, and others claim they're just lazy. But the FAA regulations "prohibit the use of certain portable electronic devices on aircraft unless the operator determines they won’t interfere with navigation or communication systems." It's long been believed that cellphones may interfere with the cockpit, especially during takeoff and landing, even though there have been no broad studies conducted to prove that and no known instances of a passenger's cellphone interfering with a flight. So, for now, the FAA prefers to err on the side of caution and continue requiring all phone go on airplane mode.