Re: Can't use GPS on Alaska Airlines

From:         jweiss@mcs.com (Jerry S. Weiss)
Organization: /usr/lib/news/organi[sz]ation
Date:         07 Sep 96 17:09:03 
References:   1 2 3 4
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In article <airliners.1996.1750@ohare.chicago.com>,
Dave Benjamin  <dbenj@slip.net> wrote:
>...
>It seems incomprehensible that aircraft avionics that MUST frequently
>fly over high-powered radio transmitters could be so suceptible to stray
>onboard RF.  My understanding is that the restrictions on in-flight use
>of electronic devices is based entirely on unsubstantiated anecdotal
>evidence.
>

The concern with on board consumer devices is that they may interfer every so
slightly with navigation systems which depend on time of signal arrival
or signal frequency. The spurious signal may be small in power, but close
in proximity to the recieving equipment. Also since the device is on the
aircraft, the error though small may be constant and over time accumulate
enough to cause a large error.

The external sources on the other hand  may be powerful, the influence they
may have on navigation systems is not constant over time as the aircraft
moves in relation to the source and thus errors not as likely
to accumulate in a systematic way.

I believe the restrictions are mostly unsubstantiated but I don't
believe they are unreasonable.  Many consumer devices emit sustantial
amounts of RF energy. Its also possible for this energy to get into
onboard aircraft transmitters, mix, amplify and be released on
new and basically unpredictible frequencies.  So additional device
screening or testing would not be a guarantee against potential
interference.

Unless there's an overriding need for consumers to operate this equipment,
I would place navigational accuracy over personal entertainment.

If someone does have a documented incident of interference, I would be
interested in hearing about it.

jweiss@mcs.com