Kapitan wrote on Jan 20^th, 2011 at 12:13am:

Well, there you have the answer then: You should never touch the trim with autopilot engaged...its fighting one against the other. If autopilot is engaged, IT controls-adjusts trim. I can imagine strange thing would happen if you touch the trim with AP engaged, (Ive never even tried it), nor thought someone would, so the bouncing could well be because of that. Another example: Its like switching autopilot altitude hold, and then try and climb or descend..."why would you do that ???" its common sense, (no need for a pilot licence on this one) either its autopilot or manual, if its autopilot..DONT TOUCH stabilizers.

Ok, I am now confused. My understanding of the 707 is that it will not do the equivalent of an ALT SEL and that you need to adjust pitch to climb to the appropriate altitude. Now if I am flying a flightplan entered either via the INS or through the FS flightplan load then I need to have the AP on. Have I misunderstood something?

BTW I just tried another flight with the same result - this aircraft unfortunately is becoming unflyable for me - back to the A300, which doesn't exhibit this sort of behaviour.