The paper proposes a method for processing and formalizing the messages of operators in automated air traffic control system on limited interaction language. The model of the limited natural interaction language is obtained, that takes into account peculiarities of the professional language of users and the internal language of the intellectual system. Texts of a limited natural language represent a surface structure of the language of interaction, expression of the internal language of interaction of the intellectual system represent a level of meaning. The surface-syntactic level of the language is specified by the structure of the noun phrases, the deep level by the trees of the syntactic subordination, in which semantic relations are established. At the same time, the links between the word forms are established not only with the knowledge of the syntax of the language, but also with the knowledge of the subject area and the semantics of the internal language intellectual system. To transfer from one level to another, it is suggested to use a multi-level description of the interaction language. Intermediate levels at transition from the surface structure of the messages to the level of meaning are noun phrases and the trees of the syntactic subordination.