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Comment by cheald | Hacker News Reader

I'd be very interested in that data, mostly because a handheld device capable of producing enough EM radiation to interfere with a cockpit from dozens of feet away (at a minimum) through metal bulkheads seems implausible, at the least. Remember that EM fields are subject to inverse-square law.

If it was possible, I can't imagine that the TSA would let us carry as much as a 9-volt battery on board. Even if it were possible, couldn't you just put shielding between the passenger cabin and the cockpit? EM radiation is line-of-sight, after all.

It seems like a giant non-issue that exists mostly due to rulemakers' ignorance.

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There are three cases that I know of, they were in an NTSB report which is not online sadly. They all involved interference with the ADF [1] and frequencies used in ILS [2]. Basically the local transmitters around airports are relatively low power so as to not interfere and they only need to 'talk' to planes that are landing, the ILS frequencies are in the 108 - 115Mhz range (just above the FM band). For a fairly long time the memory speed on PC based laptops was about 133Mhz and that was synthetically generated by clock chip running at 50 - 60Mhz on the motherboard. Sidebands from these machines, as weak as they were, were closer to the plane's reciever and so the ILS system would be unable to 'lock in' (the ILS receiver uses a phase locked loop to maintain tracking on the signal).

Anywhoo, different airports, different frequencies, and differernt ways they might interfere. Since that time laptops have gotten better (and faster, they are all generally over a gigahertz on their various busses), and radios have gotten better too.

A AT&T friend actually mentioned that AT&T had asked the airlines to ban cellphone use (back in the 900Mhz analog days) because the towers couldn't deal with a cell phone that went by a 500 MPH. However I've never been able to confirm that with any public record so I consider it hearsay at best.

[1] http://www.allstar.fiu.edu/aero/adf.htm

[2] http://www.ntia.doc.gov/legacy/osmhome/redbook/4d.pdf Redbook see pages 4-172 thru 4-174

I heard of pilots experimenting with el cheapo CD players - player goes on, needles peg. Player goes off, everything is OK.

The cell phone ban is an FCC ban, not FAA like devices during takeoff and landing - http://www.fcc.gov/guides/wireless-devices-airplanes

In the old days of analog cell phones, a single cell phone would talk to all the towers in range and hog bandwidth on every one. On the ground not many towers were in range, once you got to 20,000 feet, there were a lot. If cell phones were on on all the planes over LA, it would be like a DDOS attack.

Possibly still an issue with digital phones, but they can do a lot of smart things, modulate power, drop calls to not overload the network LOL.

> Remember that EM fields are subject to inverse-square law.

Not inside a metal tube, they're not.

This is not to say that I'm a "believer" one way or the other, but you should also think about it in comparison to the signals that the navigation equipment is trying to receive with its omnidirectional antenna. I.e., a strong CB radio 26,000 miles away. It wouldn't take any power at all to interfere with it, if the interfering signal were on the magic frequencies (which are continually changing due to doppler effects).

"which are continually changing due to doppler effects"

Doppler effects will be extremely small, since the greatest speed differential you'll see will be twice the speed of an airplane (when two planes are moving directly towards or away each other), which is not a substantial fraction of the speed of light. There will be some shift, but not nearly enough to bump a device from non-interference to interference. Or did I misunderstand something?

It might be that he is referring to Doppler VOR (http://en.wikipedia.org/wiki/VHF_omnidirectional_range), although I'm not sure how this effects interference scenarios.

Interference wouldn't alter the doppler effect, though, it would just very slightly change the frequency that would be interfered with.

In any case, I don't think any airliner flying today is relying on VOR.

If it were trivially possible for you to interfere with cockpit computers, why wouldn't terrorists be going after that? Seems like a massive, massive oversight if that were the case.

It's not an effective way to bring down a plane. The pilot would just switch to another instrument or frequency. You could land the plane without any radios or navigation. But it would raise some pulses.

In visual conditions it would be a total non-issue - GPS/VOR/IRS guidance to the airport (or radar vectors or pilotage), with a visual landing.

For an ILS approach to minimums in hard instrument conditions, it could be problematic - especially if you are off course and don't realize it. There are minimum safe altitudes on approach plates that could be violated if you are way off course (putting you into a TV tower, for example).

I'm not an airline pilot but I am pilot. I'm not aware of anything better than ILS for those types of conditions (very low ceilings and visibility). VOR/NDB approaches are non-precision approaches. The GPS I have access to does not permit a precision approach - maybe the airliners have something better.

You think it would be a problem if the ILS was sketchy in Cat 3 auto-land with ceiling/visibility at minimums ?

But the checklist should check that the ILS is alive... and if it's centered horizontally and vertically the pilots should notice.

OTOH a crafty terrorist could wait for a bad weather day, unplug the airport ILS, and set up an alternate one in a nearby building. Still, the tower would probably notice something was amiss and just say 'go around'.

I have heard that the airliners are generally all equipped with GPS units rated for precision approaches. I'd have to look at some approach plates to see how the mins for GPS approaches stack up to the ILS approaches for the same runways (I don't fly anything rated to use GPS for precision approaches).

Don't forget PAR, which generally has mins comperable to, if not lower than, ILS.

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