it is time to turn off and put away all electronic devices. on most airplanes, that announcement comes right after the aircraft door is closed. and then anything with an on, off switch cannot be powered back up until the plane cruises through an altitude of 10,000 feet. for many passengers, they understand the rule as it pertains to cell phones because they are constantly sending signals. however, many want to know why items that do into the transmit data are prohibited. like your mp 3 players, your tablets and ereaders? well an engineer with boeing says the answer is simple. the device is on the aircraft are very sensitive receivers, very specific frequencies and modes of operation. the devices that you bring on may not be operating on those same frequencies but they do have electronic emissions that can find their ways into the antennas and wiring or devices on the airplane.