An MD11 flight crew was advised enroute that 5;500 LBS of cargo included in their weight and balance document had not actually been boarded prior to takeoff. The correct data was then transmitted and programmed into the FMS.

Narrative

One hour into our flight; we were informed via ACARS that load planning had provided us with a Weight and Balance document that was in error. They had apparently failed to load 2 cans; with a total weight of 5;500 LBS. So we were actually lighter than we thought; however the center of gravity effect of the missing payload was not yet known. We contacted our Dispatcher to attain the corrected ZFW (Zero Fuel Weight) and ZFWCG (Zero Fuel Weight Center of Gravity); and also for him to run a complete Weight and Balance calculation for our flight to see if we had been inside the fore and aft CG (Center of Gravity) envelope on takeoff. We were told we had been. Next; we were going to input the corrected weights into the FMC; in order to prevent a possible CG out of limits situation; since the automatic CG control was still operating. When we input the corrected ZFWCG; the CG out of limits alert displayed. In cooperation with Flight Control and the MD-11 Duty Pilot; we decided to terminate automatic CG control; input the corrected ZFW numbers; and then reestablish automatic CG control. This was done and the flight continued safely to our planned destination.