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From: (Terrell D. Drinkard)
Subject: Re: McDonnel Douglas warns against carry-on electronic devices
Date: 30 Jan 93 22:42:47 PST

In article <airliners.1993.66@ohare.Chicago.COM> (Dennis Chamberlin) writes:
>In article <airliners.1993.49@ohare.Chicago.COM> (Kevin Driscoll) writes:
>>In article <airliners.1993.36@ohare.Chicago.COM> barr@ash.mmm.ucar.EDU (Keith Barr) writes:
>>>Wouldn't there be a change in attitude if the autopilot was engaged,
>>>which it obviously was, and if the navigation equipment was disturbed by RF?

No.  Navigation equipment tells the airplane where it is, not what attitude
it is in.  If you have somehow convinced the airplane that it is somewhere
else, it will gently guide you from where it thinks it is, to where it
thinks you want to go.  Large changes in attitude are not necessary.

>>In this case, it is
>>possible (but highly improbable) that a CD player could effect the radio
>>nav (which is forward and under the cockpit).

Not all of the nav boxes are under the cockpit.  Some are near the
antennas, some are aft under the floor.  Depends on the options selected by
the airline.

>I guess I can't swallow the idea that a passenger's CD player is going to
>find its way into nav or other avionics gear. If the manufacturer really
>said this, I interpret it as straw-grasping in the absence of other

Entirely possible for reasons that I will outline below.

>The most powerful components of a CD player are presumably the motor drive
>and audio output. Not much there. I would think that if the aircraft systems
>were so exquisitely sensitive and even if by some fault the system wiring
>in the cabin area were effectively unshielded, the resulting problems would
>be frequent to continuous, and emerge from many other sources than CD

Wiring that runs through the cabin area is not shielded, except for coaxial
cables running to antennas.  Shielding is heavy and is avoided if at all
possible.  If the passenger with the CD player is sitting next to the wire
bundle, perhaps with his player leaning against the sidewall liner, it is
very possible that either the digital or the analog signals from the player
(which is not shielded either) could alter the data moving along the
airplane's wiring.

>We all live in an environment of electrical noise from multitudes of man-made
>and even natural sources. Some of these are of much greater magnitude than
>anything that could be supplied by the batteries in the CD player. The
>normal operations of the aircraft itself emit electromagnetic energy of
>considerable power.  The cabin audio/video system is itself of much higher
>power than the CD player, although the manufacturer does control its
>installation and engineering.

That last point is a key consideration.  We test what we put on the
airplane, part of the reason those options are so expensive, but sometimes
even we make mistakes.  :-)

>I am sure that during development and manufacture, an expensive set of
>quite sensitive measurements establish the electromagnetic compatibility
>(EMC) of the aircraft with itself and both known and arbitrary outside
>sources. I believe that if the various and powerful internal and external
>sources over a broad band were ever to start talking to the sensitive
>systems, we are going to have much more to worry about than CD players.

You'd be surprised at how little EMI testing has been done on commercial
transports in the past.  This is changing as we move to more and more
complex electronic systems, fly by wire for instance.  This is called HIRF
testing. (High Intensity Radio Frequency I believe)  HIRF tests are
extremely expensive, virtually no one has the proper equipment and to my
knowledge, no standards have been mandated by the appropriate regulatory
agencies (FAA, CAA, JAA, etc).

EMI is a major argument to move to fiber optics on airplanes.  However, we
have yet to certify an airplane with fiber optics.  There are a lot of very
senior people who have yet to be convinced that fiber optics are
economically viable in the air transport industry.  They don't care what
the computer and telephone industries have accomplished.  It is an uphill
battle (you should hear their views on cables :-) but there are a few of us
fighting it.

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

Newsgroups: sci.aeronautics.airliners
From: (Terrell D. Drinkard)
Subject: Re: EMP and commercial airliners
Date: 06 Nov 93 00:24:28 PST

In article <>,
Barrey Jewall <barrey@Novell.COM> wrote:
>In <airliners.1993.702@ohare.Chicago.COM>
>(James R Ebright) writes:
>>How resistant are commercial airliners, especially the newer fly-by-wire
>>airframes, to failure due to EMP?
>The short answer: They aren't.
>1. Weight - Shielding is heavy!
>2. Cost

I read a piece (in Aerospace?) about an A330 that was hit by lightning
during a test flight.  Knocked out all the flight test instrumentation, but
the flight control computers and related systems were untouched.  Quite a
vindication for their design.

I'm not aware of any requirement to design commercial heavy transports for
EMP.  Not many commerical flights planned after the emotionally unbalanced
sorts start tossing nukes around.  We do, however, design for more
reasonable criteria, such as flying past a high-power transmitter, or
getting struck by lightning.

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

Newsgroups: sci.aeronautics.airliners
From: (Terrell D. Drinkard)
Subject: Re: Powering portables
Date: 02 Feb 94 13:27:31 PST

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."

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