According to Razbam pocket guide and many others sources[1] the Harrier AV-8B N/A has a empty weight of 13,968 lb. In game the actual empty weight is 14,804 lb even without the water (i certified to dump all of it). As you can see there is atleast 536 lb of diference, getting the weight calculation from Chuck's guide, which is the one recommended by Razbam it self, on Chuck's the weight is calculated by 14,000lb rounded on the empty aircraft, plus 300lb on pilot and equipment and another 500lb on the water. Maybe there must be a problem with the water weight not being simulated in game, which is relevant from a point of view of VTOL.