On commercial airliners, the flight crew instructs passengers to turn off notebook computers and other personal electronic devices prior to aircraft takeoff and landing. This is due to concerns over the effect of EMI on aircraft systems.
Generally, all wiring and devices in aircraft are shielded to protect them from the effects of EMI from other systems within the aircraft or external to it. But not every component can be fully protected and the civil aviation community understands very well that electromagnetic radiation from laptop computers can interfere with some onboard navigation systems potentially causing unpredictable aircraft behavior.
However, starting in November 2013 the FAA has allowed some airlines to let passengers use personal electronic devices as long as they’re kept in “airplane mode” and the cellular phone is disabled or deactivated so there are no bars visible on the screen. Passengers are still prohibited from making cell calls from aircraft in the air per FCC rules, but otherwise there are very few limitations. There are some situations which will cause the pilot to request turning off PEDs and of course, your PED will still have to be stowed during takeoff and landing.
The FAA believes that using PEDs in airplane mode allow the passenger to have an additional form of entertainment while not increasing the potential for disturbance during the flight.
When airplanes are affected by EMI (or RFI when the disturbance is high energy radio frequency), the effect can be interruption of a signal which will degrade the component’s functionality, or limit the effective performance of the device, component or circuit. The result of such an interference can be simple degradation of data to a total loss of use of the component or system.
Aircraft must be designed to withstand these effects regardless of whether potential emitting devices are not being used or not, because the source could also be a natural object or phenomenon like the Sun or the Northern Lights.
Any aircraft system or component will fail if subjected to a large enough disturbance. Today’s digital circuits are more immune to failure but when they do, it is often catastrophic. In some cases the failure may seem benign – most of us would consider a wobbly image on a monitor to be a nuisance, but on an aircraft navigation system, the results could be fatal.
The relaxing of standards should not be taken lightly but given our increased knowledge in the area of EMI and protecting critical devices from its effect, these new rules are well thought out. Furthermore, as more systems are designed to withstand the harmful effects of EMI it is likely the FAA will lighten the rules a little more to give passengers even more opportunity to use their devices freely.
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