Why do some a340 use autopilot 2 while in cruise?

[Guest giln]

Well, there's the question, why do some a340 use autopilot 2 while in cruise mode?

[Guest vrandar]

In some (most?) airlines if the First Officer is the handling pilot then s/he will use a/p2. If the Captain is Pilot Flying then s/he will use a/p1.

[Guest BenBaron]

But this has nothing to do with the system functionality, but with more psychological things (Pilot -> left seat -> left button for AP 1 ; FO -> right seat -> right button for AP).

[Guest catIIIdual]

Actually, it is rather to help the FO (pilot flying) monitor the AP behavior... I will try to simplify things a bit.First, you have two APs and two FMGC-FDs.And as BenBaron says, and since airliners are pretty well designed, FO seats on the right and uses the right-hand AP(2) button. This AP2 is associated with FD-FMGC2.Now, when AP2 is selected, FMGC2 is "master". So FMGC2 computes actively his navigation elements which are transformed into orders by FD2 and (normally!) strictly followed by AP2: the FD bars on FO's PFD are centered.Then at the SAME time, FMGC1 also computes his navigations elements, but only as a cross-check with FMGC1 elements. The 1 and 2 elements are not (but of course ALMOST!) the same. And as FMGC1 is not master, its elements are not taken into consideration to guide the plane. Therefore, since FMGC1-FD1 orders are not followed, the FD bars on CAPT's PFD are NOT centered.So if any AP pb occured, the CAPT wouldn't be able to notice it appearing, since his FD bars are "already" uncentered.There we are.Well, I just re-read myself... a bit brain-aching! haha.Hope this helps... anywaycatIIIdualLFPG.