Re: 747-400 Magnetic Detectors

From:         "Hal E. Struck x3355" <HESTRUCK%METRO@hobbes.cca.rockwell.com>
Date:         18 Aug 96 20:13:36 
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Tim,

>In a recent flight deck discussion, on a 400, I said that I thought that
>an IRS system needed an approximate heading reference for its initial
>alignment. If it doesn't of course, then there is only ONE magnetic
>compass in the entire aircraft.

On Honeywell and Litton IRUs, only the present position (lat and lon) is
required to be entered during the alignment process.  If, for some reason, the
IRU is placed into attitude mode, a magnetic heading must be entered.