More on 777 speedbrake pitch response
Aileron Drag and 777AV8R,
Thanks for your explanations. The 777 control laws are designed to compensate for the lift change associated with speedbrake extension or retraction. As the speedbrakes are extended, pitch attitude increases. As the speedbrakes are retracted, pitch attitude decreases. The intent is to avoid any significant change in load factor during speedbrake transitions. The design focussed on the airplane response during manual flight. Until now, I have not been aware that this feature leads to undersired response with the autopilot engaged. I'm curious as to which autopilot mode(s) are active when the problem occurs.
Another 777 speedbrake feature is that the control system rate limits deployment and retraction when in the air so that there is no difference in response between stepping the lever from one stop to the other and ramping it from stop to stop over three seconds.