Ask the pilot, Patrick Smith answers the question: Are cellphones dangerous to flight? First, he tells us why we have to put other electronics away during takeoffs and landings.
Before getting to cellphones, passengers should know that the restrictions pertaining to computers, iPods and certain other devices have nothing to do with electronic interference at all. For instance, laptops. In theory, a poorly shielded notebook computer can emit harmful energy, but the main reason laptops need to be put away for takeoff and landing is to prevent them from becoming 200-mph projectiles in the event of an impact or sudden deceleration, and to help keep the passageways clear during an evacuation. Your computer is a piece of luggage, and luggage needs to be stowed so it doesn’t kill somebody or get in the way.
In the case of iPods and the like, it has to do with the headphones. During takeoffs and landings, you need to be able to hear and follow instructions if there’s an emergency. That’s hard to do if you’ve got your MP3 player cranked to 11.
Key point: “I would venture to guess that at least half of all cellular phones, whether inadvertently or out of laziness, are left on during flight.”