Re: Powering portables

From: (Terrell D. Drinkard)
Organization: Boeing Commercial Airplane Group
Date:         02 Feb 94 13:27:31 PST
References:   1 2 3
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In article <>,
James R Ebright <> wrote:
>In article <>,
>Kurt W. Dekker <> wrote:
>>Regarding powering portables, I recently heard about an incident where an
>>aircraft was advised by ATC that they were several miles off their
>>assigned route, 
>Is this stuff Urban Legend (Aircraft Legend?) or is it true?

It is very true.

>Delta now lets you run scanners except at takeoff/landing... ...some carriers
>seem not to mind shavers, PCs, radios... Some seem to ban them.  There appears
>to be little consistancy.

There is a technical committee working on that.

>Given the huge amounts of RFI already existing, especially around airports, 
>(some flight paths are quite near multi-hundred megawatt xmitters) I wonder
>what the facts are.  Is there any non-anedotal, scientific information on this

Yes, but you can't have it.  :-)  Seriously, the FAA and AvWeek have
published gobs on the subject.  From an aircraft systems point of view, let
me give you my two cents worth.

The navaids come in all varieties.  Some have a coax that runs from the
antenna (typically near the midbody of the aircraft) to the box in the
rack, some (like the ADF) have a box near the antenna and run unshielded
wires in tracks under the floor and sidewalls in the passenger cabin to the
box in the rack.  The box in the rack is right underneath the first class
cabin in most airplanes.  Some aircraft have boxes in racks in the cabin
with the passengers (Fokker 100 for example).  All of you EE types should
be familiar with the possibility of cross talk between and unshielded
digital device such as a consumer-class CD player and another digital
system running through unshielded wires.

Aircraft flying by multi-megawatt transmitters are the subject of HIRF
testing, a recent and very expensive certification requirement.  However,
the inverse square law works in your favor here, where it wouldn't with a
portable computer or CD player in the cabin.  BTW, a cellular phone is
considered to be the most hazardous consumer electronic device on board the
airplane, and there are a number of documented incidents involving their
influence on the navigation systems.  I think they may well be involved in
the rash of rudder hard-overs on landing that commercial carriers have
experienced lately. (Airplane is landing, the busy traveler sneaks out the
cell-phone to confirm the rent-a-car or tell Boopsie he has arrived - BTW,
he didn't believe the cabin crew when they asked him not to use his phone
on the airplane until it arrived at the gate.)

For those who didn't catch it, airplane wiring is rarely shielded.
Shielding is very heavy (and there are several miles of wiring in every
airplane these days) and costs the airlines in terms of more fuel burned to
haul it through the air, which in turn costs the consumer more for the
ticket (or makes the airline lose more money depending on your paradigm).

>(Karl, sorry to restart an old thread...but it died last time before we
>got any really useful information.)
> A/~~\A   'moo2u from osu'   Jim Ebright   e-mail:
>((0  0))_______     "Education ought to foster the wish for truth,
>  \  /    the  \     not the conviction that some particular creed
>  (--)\   OSU  |     is the truth." -- Bertrand Russell

"Anyone who thinks they can hold the company responsible for what I say has
more lawyers than sense."