Re: Boeing landing procedures

From: (George Hull)
Organization: DirecTell L.C. - Park City, UT. - 1.801.647.0214
Date:         27 Apr 95 03:00:25 
References:   1 2
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> >I have been led to believe that for the final 200 feet before
> >touchdown Boeing aircraft use the INS system for landing as opposed
> >to ILS alone. Could someone please clarify if this is truly the case.
> No they don't.
> On the latest systems, the autopilot/autothrottle and INS are integrated to
> such an extent that when you are using one you can be considered to be using
> both. However, the autopilots (all 3 of them) would be engaged and locked on
> to the ILS if an autoland was being considered.
> Of course, not all ILS ground installations are of sufficient
> integrity to permit autolands in 'real' situations (as against fine weather
> practices).

I want to add the fact that the radio altimeter is also a critical
component of the suite of electronic devices that makes low-visibility
autolands possible.  The B-767/B-757 use three radio altimeters, three
autopilots, three ILS receivers, the inertial reference systems, three
isolated electrical systems, and two pilots to get the airplane on the
ground "automatically".  And I can say from experience that the important
milestones during the approach happen very fast . . it's quite a maneuver,
especially when it's done "for real" in dense fog.  But it's a reliable
system which improves our ability to land at our destination dramatically
(as opposed to diverting to an airport with better visibility).  During
fog season it's a good idea to fly on the aircraft which are Cat III