Is there a set procedure for this, perhaps depending on who is the PF?

It's company policy, I hear, Greg.Some airlines always use the C A/P, others may use the PF logic. Each method has its advantages.Cheers.Ian.

Thanks Ian. So what kind of advantages does it give?

Obviously you want to wear each A/P equally, so if the policy is to always use the center A/P, the autopilots should switch places during maintenance so that every A/P will have some time as "center" AP.If the autopilots do not switches places during maintenance, there has to be some sort of schedule for which A/P will be used, so that in the end they are worn roughly equally.It's similar when it comes to ignition: Usually 1 is selected for odd flight numbers and 2 for even flight numbers, or something like that.Martin767 fetishistIt's a lot like life and that's what's appealing

Interesting, thanks.

Advantage for the Centre A/P:With the C A/P engaged, any variation between the Captain's or F/O's F/D bars and the flight commands given by the C A/P will be immediately noticable (the aircraft symbol will no longer be on the F/D crosshairs... or aligned with the V Bar, where applicable)...and the pilots would be able to disengage the A/P almost immediately to prevent the C A/P flying the aircraft into the ground.Also, some aircraft have the strange(?) option whereby the the F/D bars are biased out of view for the A/P in use. E.g. If the Left A/P is in use, the Captain's FD disappears. Selecting the C A/P allows both pilots to view their respective F/D's. Oddly, however, during Autoland, no-one gets an F/D!The disadvantage of using only the C A/P is as mentioned by Martin (uneven wear and tear). However, selecting both F/D's on (as is normal practice), is exercising a lot of the circuits in the Flight Control Computers. However, wear and tear on these circuits should be minimal anyway, being solid state... It's really the autopilot aileron/elevator servos which need to be exercised regularly... and these would never(?) be swapped by maintenance for the sake of balancing out wear and tear (It would be just too labour intensive/ expensive). With the C A/P always in command, the only option to exercise the L and R servos fully is to carry out an autoland (all 3 in command). ;-)Cheers.Ian.

>these would never(?) be swapped by maintenance for the sake of>balancing out wear and tear (It would be just too labour>intensive/ expensive).Oh, OK. I was almost certain I had read about swapping the A/Ps somewhere. Not sure about which parts though. However, looking in the two AOMs I have (from different airlines) both state in their normal procedures that the center A/P should be engaged.Martin767 fetishistIt's a lot like life and that's what's appealing

Martin:May I know what airlines those are? Thanks.Regards,Russell J.

Wow, interesting stuff Ian, thanks for the insight.

Naah, err... let me just say it's a well known former racing driver owned airline, and an airline sporting marijuana leaves on the tail fins. Or maybe it's some other sort of leaf, I'm not really sure. ;-)Martin767 fetishistIt's a lot like life and that's what's appealing

Thanks Martin!Russell J. :-rotor :-beerchug :-rotor

Hi AllThis is my first post and i couldnt avoid the question, BA have full time flight directors on the B767-300s so the centre a/p isnt used except for autoland, i cant remember which but i think the left a/p is used for flight ( something to do with power supplies ) and the right is a backup, we never swap servos etc as its a messy job, they dont get that much use and never wear out they just electrically fail or leak!!!!

Greetings, (It has been a while...) From memory, there is a catch using R/L AP's, in that if the corresponding Flight Director should fail, the AP will trip out or something to that effect. It has something to do with the FD, that's all I remember. I'm sure someone can correct me here hehe.Regards, Andrew

"I'm sure someone can correct me here hehe."Mr Rockwell Collins, perhaps? :("....if the corresponding Flight Director should fail, the AP will trip out or something to that effect."Interesting. I would have thought that even though the FD was not in use on the C FCC, a failure of the FD circuits would have tripped off the A/P anyway (the FD being a part of the FCC).I had a better picture than this, but I can't seem to find it at the moment.http://members.ozemail.com.au/~b744er/767/FCC.gifI guess if the small box marked "FD Processing" failed, it wouldn't necessarily affect the preceding circuits. Cheers.Ian.

I saw in a video the L and R A/P in use during cruise ?