The project's goal is the realisation of a dedicated experimental DOE, to evaluate the effect of tolerance variation in the gear efficiency.Users of cylindrical gears in aeronautics demand continuous improvement such as increased power density, lightweight, compact size, reduced manufacturing costs, reduced noise, increased reliability and reduced operating costs.From one point of view, causes of gear failure may include a design error, an application error, or a manufacturing error. Design errors include such factors as improper gear geometry, utilisation of the wrong materials, finishing quality levels, lubrication systems, or other specifications.In this project the effect of variation of Pressure angle (α), Total cumulative pitch deviation (Fp), Total profile deviation (Fα) and Total helix deviation (Fβ) will be analysed using a full factorial DOE to analyse 4 X’s variables at 2 levels, in order to study the following Y’s effects; Load capacity (contact pressure, root bending stress), Teeth wear (pitting, scoring/scuffing), Noise (transmission error) and Power losses.With the support of Load Tooth Contact Analysis tools (LTCA) it is also possible to predict the transmission error graph with or without load and it is possible to display the grids of the bearing pattern and transmission error, with or without load, shaft angle, or run out to produce a map envelop of the expected behaviour of the gear set. Actual difficulty of these prediction tools is the lack of validation studies available. An specific numerical and experimental study will be performed in order to analyze the effect of tooth profile optimization.