Re: 757 Autoland

From:         swd_epk@afdsb.cca.rockwell.com ()
Organization: Rockwell Avionics - Collins, Cedar Rapids, IA
Date:         10 Dec 95 02:51:43 
References:   1
Followups:    1
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All weather landing capabilities are categorized by Decision Height,  the
altitude at which the crew must see the runway and take over, and, for those
with 0 Decision Height, Runway Visual Range (RVR).  The Categories are as
follows:

Category	Decision Height  	RVR

I		200 FT
II		100 FT
IIIA		50 FT
IIIB		0 FT			VARIES 100 M - 300 M (REQUIRES FULL
							AUTHORITY RUDDER)
IIIC		0			0 (REQUIRES TAXI GUIDANCE; NON EXISTENT?)


The ground facilities must also be certified for Category III approaches.  The
Intrument Landing System (Glideslope and Localizer) beams must meet certain
criteria also for quality,  freedom from multipath etc.  They are also redundant
and must meet a requirement that a standby will come on line within 3 seconds
if the transmitting unit fails.

For Category III the systems on the airplane must be shown to have less than
1xe-9 probability of producing erroneous output.  They must also be available
with the same probability over a 6 minute exposure time which represents the
critical phase of autoland near the ground,  given initial operational status.

The system must indicate its
status in terms of redundancy and the crew must not commit to a Cat III
autoland if the status isn't sufficient.  The systems also tolerate ground
station switchovers described above by maintaining flight path inertially for
a short time sufficient for the ground station to switch.  The airborne systems
are usually triplex or quad in a dual/dual configuration (ie fail in pairs).