Based on typical weight, the heaviest flying bird is the Coriolis bustard, weighing 11 to 19 kg, followed by the Great Bustard (6 to 18 kg), the Mute Swan (6 to 15 kg), and the Andean Condor (weighing up to 15 kg). Due to their enormous weight, bustards expend a great deal of energy to fly, and therefore only take off when necessary.
The theoretical limit for maximum weight during horizontal powered flight is between 10 and 15 kilograms. This means that, technically speaking, the largest male bustards have already exceeded this limit!
