The ICARO project aims to develop new, efficient, innovative and differentiated aeronautical structures in composites that satisfy the requirements of future aeronautical programmes. To this project TECNALIA brings its experience in developing future technologies that allow the rear-ends of aircraft to be optimised. However, developing aircraft structures is tremendously complicated and involves a number of difficulties that have to be faced. One of these difficulties is due to the complex process for designing aircraft wings, which has to take many very diverse factors into account, such as mechanical loads, vibrations, aeroelasticity, fluid dynamics, temperatures, viability and cost. Faced with all this, it is not easy to achieve optimum wing design, meaning that we need software that allows us to find solutions that are valid for all the above-mentioned aspects and manage to minimise the main design variables – the cost of the wing or its weight. This is why TECNALIA and AERNNOVA are developing the MDO software. The software developed by TECNALIA aims to calculate the temperatures of the heat flows that occur in the different situations in which the aircraft operates: parked on land, ascent stage, cruising and landing. The software compares the temperatures and flows calculated with the maximums and minimums that the structure can withstand and decides whether the proposed design is valid. This process is automatically repeated several times until a valid design that minimises design variables such as weight and cost is found. The finite difference method is used for the thermal module, this being a numerical method for calculating temperatures taking into account the properties of the materials, wing geometry and the thermal loads that must be withstood, such as solar radiation or engine heat.