Airbus trim system?

Date:         26 Jun 98 02:37:58 
From:         Scott Macmillan <>
Organization: Up2U
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Hello folks,  I was watching one of those 'in the cockpit' videos
the other day that featured the Airbus A320.  During the video I could
see the trim wheel moving back and forward of its own accord.
The captain explained that the aircraft has an auto trim system, the
trim being operated by the aircrafts computers.

Anyway, what I would like to know is how do the computers know how the
pilot wants the plane to fly?

eg. Lets say your in a light aircraft in level flight, then you decide
to climb.  You add power then pull back on the yoke, then trim the
aircraft to maintain the climb attitude.

Now lets say you decide to remain in level flight, but fly at a higher
air speed.  You would add power, then push the yoke forward to maintain
level flight, then trim.

If you were to do the same in the airbus, how do the computers know if
the pilot wants to climb, or if he wants to fly at a higher airspeed?

I'm guessing that the trim system is linked to the autopilot, and the
computers will know what to do by what the pilot selects on the
autopilot panel, but then, what about flying manually?

Thanks for taking the time.
Scott Macmillan
GM7OMU, IO75tv
Glasgow, Scotland, UK.