They can actually interfere with the airplane’s navigation equipment. Any electronic device with a cord can also end up “transmitting” noise (the flow of electricty through the cord makes it act like an antenea). A popular brand of corded mouse had a cord just the right length that it transmitted at the frequencies that the guidence systems use. Well, they have banned more and more devices as they have been found to interfere with electronics on the plane. Laptops must be turned off during take-off and landing because of the mice (in spite of the fact that few laptops these days use these corded mice – but rather than put the stewards in the postion of having to decide if a given laptop is “okay” or not, they just ban them all), when these guidence systems (to bring your plane in on the right runway) are used. Other devices, like cell phones, have to be off during the entire flight because they can interfere with airplane’s GPS system. Some of the devices that various electronics interfere with don’t even “transmit” per see, but the transmissions from these devices can cause a “sympathetic” flow of electricity causing errors in the electronics.

Unfortunately, people who have little understanding of electronics, physics, radio waves, etc. seem to think that these restrictions are unnecessary and punative. You’ll see a lot of very uninformed opions out there telling you that electronics interfering with airplanes is bunk. These people are very uninformed. Cable TV companies (my dad used to work for one) had to put in some extra shielding for channel 14 because this was causing problems with guidence systems. There is a rather famous case of an airplane that took off from Denver and headed for Chicago (via auto-pilot) did not realize they were off course until they were almost over Minneapolis.

some models and carriers of cell phones and avionics on aircraft use close to the same frequency’s. which cellphones and the older avionics might have problems. the newer avionics have digital tuners and are more precise and less susceptible to the interference but none the less it is just easer and safer to outlaw the use on all flights.

I am a commercial pilot and can tell when someone has not turned off their cell phone. It creates an annoying clicking and static noise in the headsets we use to communicate with Air Traffic Control. It can be a distraction.

As for the navigation equipment, there might be a very slim chance of cell phones interfering, but unlikely. Like a lot of things in aviation, its a precaution.

For those of you who saw this on Myth Busters, they were wrong like they normally are with aviation topics.

Several reasons:
1) its the law
2) cell site antennas are pointed to the horizon not up in the air so at cruse altitude you won’t get a signal
3) as another poster said they sometimes cause interference in the headphones (my Motorola phone can be heard handshaking with the cell site on my computer speakers when the phone is across the room!)
4) Lastly and most important do YOU want to sit beside some jerk talking on their cell phone for a couple of hours

BTW on board cell phones won’t bother ground based nav aids.