Re: CD players in aircraft cabin

From: (Paul Raveling)
Organization: Unify Corporation (Sacramento)
Date:         05 Feb 93 13:55:09 PST
References:   1
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In article <airliners.1993.122@ohare.Chicago.COM>, writes:
> This is a follow-up on the very interesting and educating discussion 
> about effects of CD players causing EMI problems in cabin. ... CD players
> and cellular phones are relatively low sources of EMI as when compared
> to the much greater source - lightning. ...

> (1) Will this relative lack of shielding be enough to ward off
> extraneous EMI emitted by a lightning bolt ?

	Good question.  It seems like a must-study item for anyone
	planning safety-critical electronic systems...  hopefully
	a few people will report on such studies in followups.
	A partial answer is...

> (2) To what extent does the aircraft's skin itself act as a natural 
> shield ?

	The aluminum skin of an aircraft acts much like a Faraday cage,
	shielding the interior and conducting VERY large currents
	when a lightning strike occurs.  Lightning strike protection
	is a bigger issue for all-composite airframes.  The toughest
	case may be the B-2, with a composite airframe and potential
	exposure to the high level EMP of a nuclear detonation.

> Finally since Mr. Drinkard is from Boeing I would also like to
> know how does this philosophy about shielding change with respect
> to the 777 as it will be a fly-by-wire airliner where EMI could
> affect control actuation as well.

	I'd be quite surprised if low level EMI could affect control
	systems directly.  EMI of the sort from electronic devices
	in the cabin can sometimes produce erroneous outputs from
	navigational instruments.  Couple this to the control system
	through increasingly glorified autopilots and this becomes
	a credible source of unexpected control inputs, even without
	FBW controls.

Paul Raveling