The invention refers to a method to operate an air spinning machine, in which the air spinning machine has at least one spinning unit with a spinning nozzle (2), in which a fiber strand (3) is fed to the spinning nozzle (2) through an inlet (4) during the operation of the spinning unit, in which the fiber strand (3) is imparted a twist inside a swirl chamber (5) of the spinning nozzle (2) by means of a swirled air current, so that a yarn (6) is formed from the fiber strand (3) that finally leaves the spinning nozzle (2) through an outlet (7), and in which an additive (9) is added with the help of an additive dispenser (9), at least temporarily, to the spinning unit while the air spinning machine is operating and applied on the fiber strand (3) and/or the yarn (6) or on sections of the spinning nozzle. According to the invention, it is suggested that the at least one physical parameter of the yarn (6) leaving the outlet (7) is monitored with the help of a sensor system (11) whereby, based on at least one measured value supplied by the sensor system (11) correlated with the above-mentioned parameter, it is determined whether and/or how much additive (9) was applied on the fiber strand (3) or the yarn (6) manufactured from this that passed through the sensor system (11). In addition, an air spinning machine to execute the method is suggested.