Cell Phones & Planes
Myth: The reason that you can't use your cellphone on an airplane is not because it will interfere with the in-flight instruments but because it forces you to use the in-flight phone on the back of your seat.
In-flight phones work in one of two ways. Over land they send signals to one of 135 land-based radio towers. Over the water, they send their signal up to a satellite. Hence, they are fairly expensive.
The build team had two theories as to how this myth might be true:
1. The cellphone signal masks or blocks the radio signal from the airport
2. The cellphone signal affects the navigation equipment directly
Setup
The testing for this myth was a bit interesting as it is illegal to take a switched-on cellphone into an airborne plane. They tried to get a commercial airline, chartered airline, anything, but Federal law messed up their plans. That meant that the MythBusters had to build a mock cockpit for them to test with on the ground. Grant and Tory picked up a laundry list of components from Faeth Aircraft in Sacramento, including a gyro stabilized magnetic compass system, VHF communication transceiver, navigation receiver / VOR navigation system, and GPS. Jeff Gutow, aerospace engineer, assembled their mock cockpit. After they raised an antenna above the roof of M5, they were able to get a signal from San Francisco's VOR navigation station.
The test equipment consisted of:
*Anritsu MS2721A spectrum analyzer to measure the signal given off by the cellphone.
* Faraday cage inside of a freight container to make sure their were no stray signals being measured.
* A Ramp tester to simulate the signal from the airport
* Signal generator was used instead of an actual cellphone, so that they would be able to adjust the amount of power in the signal to see how much power it would take in order to disrupt the navigation.
* VOR navigation gauge: they monitored the deflection of the needle on the gauge to see if it was being interfered with by the cellphone.
Testing inside of the Faraday cage
They first tested out their spectrum analyzer with a CD player, iPod mini, and a portable game, all of which barely registered on the spectrum analyzer. A cellphone, however, showed up as a big spike.
Next, Grant monitored the needle on the VOR navigation system while he simulated various cellphone signals. The GSM signal showed no needle deflection, even when amplified 1000x. A 800Mhz signal, however, showed major needle deflection, as did 850Mhz and 900Mhz signal.
Moving cockpit test
They concocted a setup where their mock cockpit was mounted in the pack of a pickup truck and driven around in a parking lot near the airport. They felt that a moving cockpit receiving a signal from an actual navigation station signal would be more accurate. Unfortunately for them, their mock cockpit didn't seem to like their setup -- even with the signal generator off the navigation system was going haywire.
Hawker 800XP tests
They switched to a real plane, a Hawker 800XP provided by Tom Benvenuto, VP Flight Operations, Sunset Aviation. The 800XP is a plush 8-person corporate jet filled with top-of-the-line LCD electronics. Even though they couldn't fly the plane while testing due to legal issues, they were able to test with the plane on the ground.
Grant started off with the 800Mhz signal that caused problems in the Faraday cage test. There was no interference with the 800Mhz signal or any other signal they tested.
busted The final explanation is that, even though the airplanes appear to be well-shielded against cellphone interference, there are so many different electronics in a cockpit, as well as so many different cellphones constantly coming out, the FAA doesn't want to do the necessary testing.
http://kwc.org/mythbusters/2006/03/episode_49_cellphones_on_plane.html
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