Adapting Life Cycle Impact Assessment Methods for Application in Aircraft Design

Minimizing not only costs but also environmental impact becomes more and more important in aircraft design. The environmental impact of future aircraft can be calculated in aircraft design using a life cycle assessment. Life cycle assessments are widely used to calculate environmental impacts of products during their life cycle based on the inputs and outputs that the product exchanges with the environment. For most products, these input and output flows occur on the ground. In contrast to that the major part of the emissions of an aircraft occurs during cruise in an altitude of several kilometers. In case the environmental impact of an emission depends on altitude, it is important to consider that in the life cycle assessment of an aircraft. Therefore this paper investigates to what extent existing life cycle impact assessment methods consider the effects of altitude dependent emissions and if they have to be adapted to be able to deal with the special requirements of life cycle assessments of aircraft. The results of that investigation show that the effects of contrails and cirrus clouds as well as certain altitude dependent environmental impacts of certain emissions are not sufficiently covered by existing impact assessment methods. Therefore it is proposed how existing methods for an altitude dependent calculation of the environmental impact of emissions can be integrated into existing impact assessment methods. Finally it is analyzed how this integration affects the results of a life cycle assessment of aircraft using the medium range aircraft Airbus A320-200 as application example. It is shown that the integration of contrails and cirrus clouds as well as NOx emissions leads to a considerable increase of the environmental impact of aircraft. The single score of the ReCiPe method expressing the total environmental impact rises by 108 %. The percentage of contrails and cirrus clouds on the overall environmental impact rises from 0 % to 32 % while that of NOx emissions rises from 8 % to 24 %. The proposed adaption of existing life cycle impact assessment methods allows to improve the accuracy of the life cycle assessment results of aircaft and to consider new effects in environmental aircraft design optimization concerning, for instance, flight mission profile or emissions that have previously been wrongly rated as safe