Across industries, project complexity has been increasing over decades evolving to be a determining factor for the success or failure in project management. In this context, many studies have demonstrated a significant correlation between an appropriate evaluation of project complexity, the decision for a well-fitting project model and its resulting economic effects for its execution and outcome. At major airlines, however, snapshot experiences of project management practitioners have indicated difficulties in achieving effective decision making for both an adequate project model and its administrative budgets based on individual evaluation of project complexity resulting into controversial debates amongst project stakeholders. Aside the natural subjectivity in perception, an ambiguity in key terminology (e.g. the meaning of complexity itself, complex vs. complicated) and politically influenced motivations were observed as fanning factors, too. Eventually, negatively affected time of delivery, exceeding demand for financial means and resources, and inherited risks on project success had been reported consequences. Therefore, this study was conducted with the primary objective to identify an appropriate approach for project complexity assessment (PCA) that shall help airlines to take more effective decisions towards an efficacious project model. The secondary objectives were to qualify the potential in the airline industry for an improved organizational performance by PCA and to clarify key terminology. The objectives of the study have been accomplished by conducting a diligent literature research, an explorative survey of 20 airlines, the utilization of the Helmsman Complexity Scale accompanied by expert interviews and the evaluation of common PCA methods (PCAM). Consequently, the identified situation in airline practice of both its project complexity and its utilization of PCAM have revealed the potential for many airlines to considerably enhance their decision processes and project economics by employing the conclusively proposed PCAM. However, limitations apply: comprehensive PCAM can´t avoid subjective components and thus can´t entirely prevent discussions caused by perception and individual experience. While this research has been subject to the common airline category of so-called Full-Service Network Carrier (FSNC) it is likely applicable for most major airlines of all categories. As an outlook for further research, further developing, testing and calibrating the outlined custom PCA model by a representative set of airlines may substantiate its applicability in practice.