.adversely affect the functioning of an airplane's Radar with the distinct possibility of it crashing then why do terrorists bother with knives, bombs and guns?!.
I've worked with a weather radar (a very advanced one) and it has no concerns about a cell phone operating in a different frequency, with a different modulation and the radar is a Level C system, which means even if it fails, the aircraft's flight is not adversely affected. I work with an FMS now and yet again we have no worries about one cell phone transmitting. Cell phone frequencies are covered during the EMI/EMC testing of airborne equipment. There are good answers above me giving the valid reasons, if some doofus chose to give them TDs and you opt to disregard their wisdom, then cant help it.
Mobile telephones do not interfere with aircraft systems. As a result, a terrorist trying to use a cell phone to crash an airplane would be wasting his time. There are anecdotal reports of alleged interference, but nothing that withstands a scientific test. In fact, pilots sometimes use their cell phones in the cockpit—and if the phones really did interfere with aircraft systems, using them in the cockpit would make that very obvious, very quickly. The real reason cellular telephones are banned in flight (in the U.S.) is that there is an FCC regulation that prohibits their use. The regulation was originally put in place because it was feared that cell phones in the air would overload base-station networks on the ground. We now know that this isn't true, but the regulation remains in place. There's also a FAA regulation that prohibits the use of electronic devices in the cabin during flight unless the operator (that is, the airline) has determined that they are safe. Airlines never bother to test electronic gadgets, so they just prohibit them instead, at least during takeoff and landing. However, airlines don't follow the regulations entirely, because they still allow them during cruise flight, which is a violation of the same regulation that bans them during other phases of flight. Sometimes cell phones can produce an audio buzzing noise in nearby audio equipment, such as stereo systems or headphones. Very close proximity is required for this (a few feet), and it's just an irritation, not a compromise of avionics systems or a safety issue. In any case, until and unless the regulations change, cell phones can't be used in flight. The relevant FCC regulation is 47 CFR § 22.925; the relevant FAA regulation is 14 CFR § 121.306.
Cell phone use on board airplanes has very little to do with aircraft radar or navigation. Celular telephones are regulated by the Federal Communications Commission, not the FAA, and it's the FCC rules that say that cell phones cannot be used while in flight.
You obviously know nothing about airplanes or cell phone technology. Whether the on-board radar works or not isn't an issue because it is only used for weather avoidance. In scientific studies cell phones have occasionally been linked to interference with certain navigation systems (I've experienced it myself), but the results have generally been inconclusive or negative. That aside, navigation and communication problems very rarely cause airplanes to crash. The main reason cell phones cannot be used while airborne is that their range increases dramatically with altitude, and being able to trigger multiple cell tower relays creates havoc within the cellular system, particularly if a lot of airborne phones are being activated at once in the same region. It's all about the cellular network.
It's not so much that mobile phones adversely affect aircraft systems. It's just impossible to thoroughly test every mobile phone for interference, so there is a ban to mitigate that risk altogether. The bigger issue is that cellular networks were made to be ground-based, having a limited number of towers within the line of sight of the phone. There could be major telephone network issues if thousands of people started making phone calls from 35,000 feet to a system designed to be used from the ground. EDIT: I'm not sure what you are looking for from your question because it appears that several people gave you good answers that you aren't satisfied with. Here's the clarification why they are banned: 1) FAA regulations only allow a few electronic devices to be used in flight, such as pacemakers and hearing aids. All other devices require the airline to make the determination that the device will not cause interference with airplane communication and navigation systems. See FAR 91.21: ecfr.gpoaccess /cgi/t/text/tex Consumer electronics that don't use any kind of radio waves have been deemed safe. Airlines shy away from devices that do rely on radio waves because there are many different products and they do not want to take on the liability of making the determination of which ones can and can't be used. Adding wifi to airplanes is actually a pretty major step. 2) FCC regulations prohibit use of cellular telephones while not on the ground due to concerns of how it will affect the cellular network. See 47 CFR 22.925: frwebgate2.access.gpo /cgi-bin or the FCC consumer notice: fcc /cgb/consumerfacts/cel
