July 2011

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Arlene Fox

By that argument, you don't need to ban guns. "Just turn them off."

If a cellphone in use can take down an airplane, what's to stop terrorists from activating cellphones and other dangerous devices while in flight?

Now you've got me real scared!

John F. Opie

Hi -

Because people don't want to give them up entirely.

The reason that electronic devices that emit radio waves are not allowed to be turned on in flight is that while most electronics in commercial planes are shielded, there are gaps in the shielding that permit radio wave leakage throughout the airplane. Given that the internal shape of planes - complex ellipsoids - result in the propagation not only of the actual frequencies, but also multiple harmonics of the same, it is almost impossible to effectively shield the in-board electronics from this sort of radio energy.

The problem is that some of the electronics on planes are highly sensitive to radio energy, especially electronic compasses (compassi?). There have been two documented cases of airplanes ending up on the wrong course due to errant radio emissions from internal sources. Like I said, you can shield the electronics, but it's not a simple matter of a bit of aluminium foil and Bob's your uncle: you have to worry about harmonics of these signals obscuring or at least getting mixed in with legitimate signals, resulting on serious navigation problems (like a pilot thinking he's dialed in the right course flying over the Pacific, while in reality he's heading into Soviet territory: that is one of the reasons that the one KAL flight was shot down by the Soviets!).

It's a great deal simpler to simply require by law that the devices be turned off whilst in the plane. You don't need to ban them: just turn them off.


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