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DL_Mech
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Posts: 2083
Joined: Fri Feb 18, 2000 7:48 am

747 Classic Autopilot

Mon May 22, 2000 3:26 am

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.
 
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DL_Mech
Topic Author
Posts: 2083
Joined: Fri Feb 18, 2000 7:48 am

Some Photos

Mon May 22, 2000 3:52 am

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.
 
VC-10
Posts: 3546
Joined: Tue Oct 26, 1999 11:34 am

RE: 747 Classic Autopilot

Mon May 22, 2000 5:19 pm

Customer option
 
Buzz
Posts: 694
Joined: Sun Nov 21, 1999 11:44 pm

RE: 747 Classic Autopilot

Mon May 22, 2000 11:37 pm

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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