Abstract: There are always narrow topological faces on the CAD model of aircraft structures, which is
prone to lead a series of engineering operations to fail in the manufacturing process of part. To solve this
problem, an automatic narrow face error detection technique for CAD model based on the analysis of
parameter district boundaries is proposed. First, the common narrow faces of aircraft structural CAD
model are depicted and classified. And, based on the geometrical characteristics and the engineering
requirements, the narrow face error is defined. Second, the effective parameter district of each
topological face on the CAD model is computed. Third, the narrow district is constructed according to
reflex points. After that, the length and the width are calculated to judge if the topological face is a
narrow face error. Finally, the algorithm flow of this technique is given and implemented. The
experimental results are showed to prove that the presented method is both correct and effective.

Key words: CAD model error, error detect, CAD model repair, aircraft structure, NC machining;
narrow face error