A method and a device determines an air mass flow flowing through a ram air channel having disposed therein a feed device adapted in a first operating state of the ram air channel to feed air through the ram air channel and further adapted in a second operating state of the ram air channel to be set in rotation by an air mass flow flowing through the ram air channel. The method includes the step of detecting an actual operational characteristic of the feed device that is characteristic of the air mass flow flowing through the ram air channel in the second operating state of the ram air channel as well as the step of determining the air mass flow flowing through the ram air channel on the basis of the detected actual operational characteristic of the feed device.