Fliers Must Turn Off Devices, but It’s Not Clear Why

Re:Fliers Must Turn Off Devices, but It’s Not Clear Why by ChuckMcM on Sunday November 27, 2011 @11:35PM (#3284552)

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

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Re:Fliers Must Turn Off Devices, but It’s Not Clear Why by RockyMcNuts on Monday November 28, 2011 @01:42AM (#3284868)

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.

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