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I'm going on a long flight tomorrow, and would like to be able to use my laptop during the journey.

Wireless devices like WiFi and bluetooth interfere with airplanes instruments, and shouldn't be used on flights.

If my laptop does not have a physical rf-kill switch, is it sufficient to just ensure that the relevant modules do not get loaded?

If so, is that always safe, or does it vary between different hardware?

My particular situation, is a Samsung NC10 netbook. Atheros 5k wireless hardware. Debian sid with kernel 2.6.30-1-686. However, I think it'd be interesting to know the answer to this question for the general case; not just my specific case.

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"Interference" they've always said. And then, curiously, Airtran starts offering in-flight Wi-Fi... –  hyperslug Jul 31 '09 at 18:54
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...and Ryanair allow in-flight mobile phone calls. However, as I'm hurtling through the sky in a big metal tube, thirty thousand feet above the endless blue waters of the Atlantic, I'll err on the side of caution :) –  SpoonMeiser Jul 31 '09 at 19:04
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It always was purely speculative. Its just that your really don't want any "extra" airliners falling out of the sky... I am curious to know what (if any) testing and modifications Airtran did with the avionics before they started. –  dmckee Jul 31 '09 at 19:04
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1 Answer

Modern airplanes are no longer susceptible to the low powered interference these devices emit but the aeronautics agencies would rather be safe than sorry. So they are unwilling to change the rules. I would not worry too much about it. If you want to err on the side of caution disabling the driver should be sufficient.

For the wireless adapter type:

for i in `find /sys -name "rf_kill" ; do echo 1 > $i ; done

Then to turn it back on:

for i in `find /sys -name "rf_kill" ; do echo 0 > $i ; done

Courtesy of www.lesswatts.org. Not sure if this works for Bluetooth devices as well.

You could also try looking in the BIOS to see if it can be disabled from there. This may be a simpler solution.

The Discovery show "Myth Busters" did a segment on this very issue. They ran tests on very old aeronautics equipment they had isolated using a Faraday cage. They found that modern cell phones did cause enough interference to adversely affect the equipment.

They even convinced the FAA to allow them to test a grounded plane. All the aeronautics instruments were sufficiently shielded and they found no interferience even with a high powered transmitter.

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The rf_kill malarky is different to unloading the module. 'find /sys -name "rf_kill"' doesn't find anything on my laptop, so unloading the module is the only option I believe I have. Does using rf_kill do anything that unloading modules does not? –  SpoonMeiser Jul 31 '09 at 19:53
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Hmm, is it possible there is a newer module? Initial support for rfkill was added to the ath5k driver back in January. Rfkill is the preferred way to ensure turning off the radio in Linux. There's no consistency among hardware vendors. Some turn the radio on as soon as there is power and the driver simply manages the device. –  Kenneth Cochran Jul 31 '09 at 20:38
    
I know there's been work done, but I don't believe that it has made its way into the main kernel yet. –  SpoonMeiser Jul 31 '09 at 21:49
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rfkill as a standard mechanism for all drivers was added with kernel 2.6.31. It's accessed through a tool aptly named rfkill. See mjmwired.net/kernel/Documentation/rfkill.txt and packages.debian.org/de/sid/rfkill . For older kernels, the mechanism to disable WiFi, bluetooth etc. is different for each driver (hence the rfkill system). –  sleske Jun 7 '10 at 22:48
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