Re: Stand-by instruments (was external inspection)

Date:         17 Jan 99 02:37:42 
From:         "John Weiss" <jrweiss@seanet*NOSPAM*.com>
Organization: Seanet Online Services, Seattle WA
References:   1 2 3 4
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Phil. G. Felton wrote in message ...
>Well it wouldn't work in a pressurized plane anyway.  I'd be surprized
>if all the instruments on the modern planes were all electric.  Even on
>a light plane like a Cessna there are vacuum driven gyros and elect
>driven gyros to prevent total system dropout in case of a power failure.
>There's usually an alternate static source provided (external static
>ports do get blocked in icing conditions sometimes).  Of course you have
>to recognize when you need it!

Even in the 747-400 the standby gyro is electrically powered.  It can be run
off the standby power system (including the battery), but so can the Capt's
main CRT displays and instrument lights, the backup Flight Management
Computer (a mode of the FMS-CDU), 2 of the 3 Inertial Reference Units, 1
Transponder, 1 VOR and 1 ILS.  The standby Airspeed and Altimeter are driven
by separate pitot and static ports than the others, and only their lights
are electrical.

It would take a LOT to go wrong, beyond 4 generators failing, to get to the
point where only the standby instruments were available...

John R. Weiss
Seattle, WA
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