From: firstname.lastname@example.org () 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).