The topic of the article is the aircraft optical-electronic systems for land-based objects sighting; those systems employ algorithms for solving of the problem of automatic discrimination of the objects defined by the mission input data according to the reference information. Random inaccuracies of the navigational data automatically reaching the radar range perimeter of the aircraft as well as inaccuracies of an adequate aspect angle development from the side of the sighting coordinator lead to the fact that an object entering into a camera's field angle has a random character. This fact has a decisive influence on the effectiveness of the use of an aircraft complex of integral guidance in respect to the specified object. For this reason, the probability estimate problem of object sighting by an airplane system in case of automatic reaching the radar range perimeter is topical and significant. The probability of an event, in which the object entering into the coordinator field angle on the radar range perimeter is specified by an equivalent probability of the event, in which the inaccuracy module of the coordinator's angular orientation with reference to a target does not exceed the value of a half of the coordinator's angular field in the vertical passage. The object sighting probability dependences of the coordinator's field angle and the radar range perimeter's distance are the following: the dependence rises with an increase of these values and falls with their decrease. An aircraft with the sighting system of a smaller field angle must be placed at a larger distance in front of the object for support of the same probability level. And, vice versa, a larger field angle of the coordinator supports a smaller distance of the radar range perimeter's location. The dependence of the probability of the object entering into limits of the sighting system field angle of distance is presented. The results of the article can become a basis for the techniques of analysis of a sighting system's functioning in discrimination of an object's defined multitude in different conditions of the aircraft automatic flight