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This study addresses the issue of the aviation sustainability which has become an essential issue for the aviation sector which is a direct polluter of the Earth's atmosphere through its emissions of CO₂, NO_x and other particles, noise and the creation of contrails contributing to the greenhouse effect. More than a decade ago, apart from aeronautical noise, reducing environmental impact was not a top priority for the aeronautical sector. In the last decade, aircraft manufacturers and airlines have faced increasing pressure from governments, customers, and investors to act assertively on environmental issues and to promote and achieve sustainable environmental goals and targets. It is considered that to reach audacious sustainability objectives in the next decades, new regulations and penalties will be applied to air transport operators and then new aeronautical technologies must be introduced to maintain the activity of this sector. This will have as consequence a rather complete renewal of civil aviation fleets in the next decades. Then airlines will soon be faced with the necessity to implement heavy investment programs for the renovation of their fleets, entailing significant financial costs which in turn could lead to higher ticket prices and a contraction in demand. The survival of airlines during this apparently turbulent period could be put seriously to the test.In this paper, the resilience of an airline in the face of such high investment needs, but also in the face of the uncertainty with respect to future operational costs and demand, is analyzed. A long-term fleet planning period is considered for a generic airline with her initial fleet, operated network, and demand. A scenario where new national/international regulations are introduced with two milestones: one from which environment non-compliant aircraft operating will be subject to a penalty and one from which such aircraft will no longer be allowed to operate. The sustainability conditions attached to such a fleet renewal program are established and financial and operational sustainability objectives are discussed. Besides the assessment of extreme decision scenarios, a long-term fleet investment optimization problem is considered to optimize the assets of the airline and guarantee revenue. Dynamic programming is used to face the temporal and the uncertainty dimensions of this problem.

The paper is organized as follows: the considered problem and its context are introduced, long term as well as short term sustainability conditions are established for the airline according to the timing of the enforcement of new environmental regulations and fleet investment, sources of uncertainty and possible scenarios are analyzed, the fleet investment optimization problem is formulated, and a solution scheme is developed. The proposed approach is illustrated with a small-scale case study where the impact of the timing of the environmental regulations over the resilience of the airline is assessed, then providing guidelines to authorities in this field.

Keywords: Aviation sustainability, Airlines Resilience, Fleet Renewal, Dynamic Programming.