1. A process for direct fabrication of at least one part at a predetermined position on a structure, said process comprising the following successive steps: a) scanning, via a three-dimensional scanner, the structure in a region of the predetermined position; b) comparing, by a central unit, a virtual surface mesh of the predetermined position with a real surface mesh of said predetermined position, said virtual surface mesh being calculated by the central unit from modeling data recorded in a first database, and said real surface mesh being calculated by the central unit from data obtained subsequent to the scanning carried out in step a); c) determining, by the central unit, the existence of one or more gaps between said two meshes, said one or more gaps representing joint clearances in the structure; d) calculating, by the central unit, data for modeling an inserted part having dimensions which fill up said one or more gaps calculated in step c), to obtain a model of the inserted part; e) merging, by the central unit, a virtual model of a part, linked with said predetermined position recorded in a second database, with the model of the inserted part calculated in step d), to obtain an adjusted model of the part having geometry adjusted to the structure in the region of the predetermined position; f) fabricating an adjusted part based upon the adjusted model calculated in step e) by depositing material with a deposition system directly on the predetermined position.