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, of the structure in the 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 on the basis of modeling data recorded in a first database, and said real surface mesh being calculated by the central unit on the basis of data obtained subsequent to the scanning carried out in step a); c) determining, by the central unit, the gaps between said two meshes, said gaps being representative of joint clearances which are present in the structure; d) calculating, by the central unit, the data for modeling a part, called an inserted part, the dimensions of which fill up said gaps calculated in step c), in order to obtain a model of an inserted part; e) merging, by the central unit, of 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), in order to obtain a model of a part, called an adjusted model, adjusted to the geometry of the structure in the region of the predetermined position; f) fabricating, by deposition of material by a deposition system, an adjusted part at the predetermined position on the basis of the adjusted model calculated in step e).