**3.1. Cost-benefit analysis (CBA)**

Cost-benefit analysis (CBA) may be a valuable tool for cases where a large number of investments in the air transport sector have to be ranked against each other and define a strategic investment plan in order to influence decision-making process [12]. CBA is an analytical method that is frequently used in ex-ante analysis and is applied to investments into the transportation sectors in order to provide evidence so decision-makers can justify their decisions [12].

In Ref. [13], the role and position of CBA in the transport planning process are presented, partly based on a survey of a number of countries where CBA plays a formalised role in decision-making and is concerned with the appraisal situation in the overall decision-making process and if CBA appraisal results actually influence decisions. Elliasson and Lundberg [12] confirmed that since decision-makers are knowledgeable in regard of CBA appraisals, they take this into account when selecting public investments early in the decision-making process.

On the other hand, there are many researches that claim that CBA does not support decision-making process in a sufficient way. Odeck [14] claimed that most of the variables determining decisions are included in CBA evaluation, but the decision-maker takes account of them in nonmonetary units rather than in a composite benefit-cost ratio or net present value. Furthermore, as in Ref. [14], it is also supported that CBA does not matter in stakeholders decision making, but its components matter in a nonmonetised form [14].

In Ref. [15], 10 large transport projects in eight countries that had benefited from EU Cohesion and ISPA funding are examined, and the not extended contribution of all the relevant economic impact analysis tools, especially such as the CBA framework and multi-criteria analysis framework, was identified. Mouter and Annema [16] noted that the debate between many economists claim the fact that CBA is an overestimated framework not so extended and not so useful in the stakeholders decision making process and this is a major problem in multiagent decision making as it results in big debates between the different stakeholders and agents about the positive and negative effects of CBA results.
