Re: Navigation Question

From: (FMCDave)
Organization: America Online, Inc. (1-800-827-6364)
Date:         04 Oct 95 22:57:25 
References:   1
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  or MIME structure (Joe M Wilson) wrote:
>I recently had the extreme pleasure of riding in the Cockpit of an A320
>Airbus for an entire flight.(Ottawa to Toronto).I wondered if someone could
>explain to me the basics of the Airbus's Inertial Navigation System. I Didn't
>want to bother the captain or the co-pilot with the question at the time.I
>had asked so many questions at the time I feared they would kick me out of
>the cockpit.

While this answer isn't for the A320 exactly, the basics of most glass
airplanes is the same.  The inertials are not really the navigator, they
are sensors.  The A320/330/340 737/3--+/757/767/747-400 MD11 and such all
use a multisensor area navigation system.  The IRSs are used as an input
along with radios (VOR/DME/LOC) and possibly GPS.  The area nav system is
generally a FMS but can sometimes be an INS.

For the 747-400, there are three Inertial sensors and the FMS "mixes" them
into a common position.  This is the basic position solution for
navigation.  If there are other input sensors available, they are used to
compute a correction factor to the inertial position.  In the case of
radio, the radio position is used to put a correction bias into the triple
mix position. In the case of GPS, if the sensors have a good solution,
then the GPS solution is used.

David Allen
Project Manager, CNS/ATM
Opinions are mine and not Boeing's