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747 Classic Autopilot  
User currently offlineDL_Mech From United States of America, joined Feb 2000, 1951 posts, RR: 9
Posted (14 years 4 months 2 days 15 hours ago) and read 1987 times:

Does anyone know why some 747 Classics have three autopilot "bat-handles" (A,B,C) while others have only two? The C autopilot switch is usually covered up or removed altogether. Did Boeing change the 747 from three single channel autopilots to two dual channel ones? Are these planes CATIII? Fail passive or fail operational? Thanks for the answers.


This plane is built to withstand anything... except a bad pilot.
3 replies: All unread, jump to last
 
User currently offlineDL_Mech From United States of America, joined Feb 2000, 1951 posts, RR: 9
Reply 1, posted (14 years 4 months 2 days 15 hours ago) and read 1923 times:

Three autopilots (A engaged) Left side
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Photo © Craig Murray

Three autopilots (A engaged) Right side
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Photo © Wilfried Schnetzler

Two autopilots (C switch removed) Left side
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Photo © Jeremy Holdsworth

Two autopilots (C switch covered up) Left side
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Photo © Omar Zekria

Two autopilots (B switch removed) Right side
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Photo © Marco Blauwhof




This plane is built to withstand anything... except a bad pilot.
User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3701 posts, RR: 34
Reply 2, posted (14 years 4 months 2 days 2 hours ago) and read 1893 times:
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User currently offlineBuzz From United States of America, joined Nov 1999, 697 posts, RR: 21
Reply 3, posted (14 years 4 months 1 day 19 hours ago) and read 1868 times:

HI DL mech, Buzz here. Sir VC10 is right, whoever ordered that one wanted one more autopilot aboard. All our Classic Lumps (-100's) are retired, we have some ex-Qantas (-238's) and they're 2 autopilot ships.
The triple autopilot is Boeing's way of ensuring Cat 3b landings. The 737-300's are a Cat 3a animal, with 2 autopilots.
The A320's we have are only a "2 autopilot" affair, but each is a 2 headed monster : command, and monitor. So 4 channels have a death grip on the ILS in a coupled approach.
THe difference between Cat3a and Cat3b? Well, Cat3a (737 stuff) has a 50 foot ceiling (half a wingspan up) and 700 foot visibility (you can see 4 seconds ahead of you). The 737 doesn't use rudder for autopilot work.
Cat3b has zero foot ceiling (can't see your shoes due to fog) and 400 foot (OK, i forget exactly) visibilty. Figure that you land about 120 mph..... 176 feet per second...... the airplane has to keep you straight on the runway.
Ever wonder why we mechanics go to school a lot? When we make mistakes the press thinks it's a big deal or something! (grin)
g'day
Buzz Fuselsausage Line Mechanic by night, DC-3 Crew Chief by choice


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