It is researched the operation of an aircraft on the modes of horizontal flight with the maximal duration. Extremals of the functional on the basis of the traditional form of the integral acquired with respect to the equations of motion of a material point with the changeable mass by I.V. Mescherskiy (1893-1897), T. Levi-Civita (1928) with the addition of the entropy of the controlling element's of the active system individual subjective preferences has been obtained as a solutions of the variational problem on the necessary conditions for the extremums existence in the view of the system of the Euler's-Lagrange's equations. Canonical distributions of the preferences and the optimal mode of the horizontal flight for the maximal duration have been got also in the case when the extremal speed cannot be reached or realized for one reason or another. The control in such a case implies preferences of the greater derivatives or differentials as the functions of effectiveness. The optimal modes of operation are being obtained on the basis of the subjective entropy extremum only and no other restrictions, except normalizing condition, has been imposed in the problem formulation. The necessary calculations are conducted. Plotted corresponding diagrams.
