Do cell phones really interfere with airplane instruments?

i have heard that they *really* interfere with the cellphone system. if they interfered w/airplane systems in any serious way, the stewardesses would come by and make sure they were off.

I heard a few years ago they were looking into allowing cell phones, then they did some research, and decided against it. Not sure where I heard this. But I think there is some small but real issues with interference... though I suspect it wouldn't generally be a problem... but "generally" isn't good enough for airplanes. I think the iPod stuff has no danger, but still makes sense... i.e., next gen iPods may have cellphones or other wireless transmission builtin. So to be simple they just ban everything electronic.

Now that I think about it, the really weird part of this is that it's all on the honor system... meaning they don't do any more than a theatre that tells you to "please turn it off," but I'm sure some people fail to do this, and if it did pose a real danger, you think they'd have a more strict system.

Cell phones DO interfere with Airplane instruments, particularly Navigation instruments.

Have you ever set your phone next to a speaker, got a call, and heard that peculiar 'buzzing' noise come through the speakers? That's exactly what the phone does to any other electronic device around it. You are putting peoples lives in danger by using your phone on a plane.

Some airlines actually allow cell phone use. So it can't be that bad. http://www.cnn.com/2006/TECH/12/21/wired.airlines/index.html

As a recent road warrior, I can tell you that it is mostly precautionary.

Pilots can "tell" if someone has a cell phone on, although I've been on many a flight where some executive thinks he's above rules and breaks out the crackberry to answer a few emails.

Also, I've heard a conspiracy theory that it's a preventative measure against terrorists indicating where they are in taxi lines/queues.

cellular phones attempt to associate with any cell tower within range. though a call is only ever actually being routed through one tower at a time (i think. not totally sure about that.), there's still data traffic passing around as your phone looks for other nearby towers to fall back on if the current tower drops out. when you're walking around on the earth, there are all sorts of obstructions (not the least of which is the earth itself) which restrict your range, and your phone might only be able to "see" two or three towers. since most people make phone calls while on the ground, the cell network was design to allow the phones to maintain as much contact as possible with as many towers as possible in order to maintain the highest quality connection.

but when you're up in an airplane, your phone has line-of-sight on dozens of towers. so it's making a lot more connections than normal, and passing a lot more data. since any network has a fixed bandwidth (bandwidth = amount of data that can travel over the network in a given amount of time), a sudden increase in data traffic must necessarily be accompanied by a decrease in total network speed. if everybody had their phone switched on while airborne, it would be quite possible to crash entired portions of a given cell network due to the increased traffic.

regarding my sources, i have a friend who flies for united and insists the no-cell rule is garbage.

regardgin shank's mention of interference with speakers, that's true. but it's more an indication of the lack of shielding in most speakers. also notice how close you phone must be to hear that interference... last time i checked, there was no navigation equipment installed in my armrest. that interference, like all point sources of electromagnetic radiation, obeys the inverse square law which states that the power of an electromagnetic wave is inversely proportional to the square of the distance from the source of the wave. if you move the phone twice as far away form the speaker, you get one quarter the interference. move it three times as far, you get one ninth the interference. and the closest seat to the cockpit is maybe ten feet away? not even slightly close enough.

see http://hyperphysics.phy-astr.gsu.edu/hbase/forces/isq.html for more on the inverse square law.