[RFI] RFI Digest, Vol 39, Issue 7

Tom Cox tomcox at iquest.net
Wed Mar 8 18:30:55 EST 2006

I've seen a few, important observations on this topic in the threads 
I've been following.

First, using a cell phone at cruising speed and altitude in a commercial 
airliner is usually pointless, because multiple cell sites will be in 
range of the call at the same time, and none of them is likely to hold 
it long enough to complete it. The probable lack of success would seem 
to be as strong a discourager of cell phone use in that context as any 
prohibition would be.

Second, I'm told that the critical times for avionics, and the most 
dangerous time for an aircraft in general, are during takeoff and 
landing. During IFR conditions, I can see prohibiting cell phone use 
even if the odds are higher than a million to one against the phone 
causing problems. However, as it has also been pointed out, the RF 
environment within a few hundred feet of a runway at most commercial 
airports is already saturated across much of the spectrum.

If a 200 mW cellphone with a notoriously inefficient antenna aboard an 
aircraft can jam the avionics, how about a 30-Watt trunked, 800 MHz  
mobile do in an airport maintenance truck, with a gain antenna on a 
metal roof, as the plane flies past it at a few hundred feet, on final? 
I don't travel a lot, but I have been around several airports, and there 
is no shortage of cell site towers, probably also carrying kilowatt 
paging transmitters with high-gain antennas, and even some broadcast 
radio and TV transmitters, close enough to have very high signal 
strength inside the aircraft for seconds at a time.

If such an equipment vulnerability can be demonstrated, the RF 
susceptability of the affected equipment needs serious work, or it has 
no business in a mission-critical application like an aircraft, with or 
without cell phones.

Finally, if I required one-in-a billion odds against death, or even one 
in a hundred million, or even one in TEN million, before I would 
undertake to do something, I'd be left with very little to do. I'd 
probably die from immobility. The only people with really good odds 
against death in any context are the people who are already dead. Until 
I join that cohort, I'll... take my chances.

Tom, KT9OM

rfi-request at contesting.com wrote:

>Today's Topics:
>   1. Re: RFI Digest, Vol 39, Issue 3 (Martin, AA6E)
>Message: 1
>Date: Tue, 7 Mar 2006 22:20:26 -0500
>From: "Martin, AA6E" <martin.ewing at gmail.com>
>Subject: Re: [RFI] RFI Digest, Vol 39, Issue 3
>To: rfi at contesting.com
>	<6a2b366e0603071920u25f8e666p4213dcc06128d479 at mail.gmail.com>
>Content-Type: text/plain; charset=ISO-8859-1
>The *probability* of causing an accident with your cell phone must be
>very low.  And probably the stars have to be aligned just so (using
>certain comm freqs, nav aids, etc. in the cockpit, with marginal wx
>and so on).   So maybe it will only happen once in a million times. 
>That's not useful for the bad guys, but it may be enough reason to
>prohibit cell phones.    Your seat-mate wants to call the office: What
>odds of a crash would you say are acceptable?
>Even if you accept 1 in a million for yourself, how do you feel that
>that might be 8 downed planes every year? (8.4 M flights in 2003,
>73 Martin AA6E
>On 3/3/06, Tom Cox <tomcox at iquest.net> wrote:
>>This was my comment on this topic on another list, where there is also lots of interesting discussion:
>>I certainly don't want to put any flight I'm on in jeopardy by using a
>>cell phone. 
>>Tom, KT9OM
>>RFI mailing list
>>RFI at contesting.com
>martin.ewing at gmail.com
>RFI mailing list
>RFI at contesting.com
>End of RFI Digest, Vol 39, Issue 7

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