To date, commercial aviation contributed approximately 4 % of global anthropogenic climate change through the emission of greenhouse gases during flight and operational non-CO₂ climate effects. Over the last few years, numerous aviation-related organisations have set goals to reduce aviation’s climate impact. These goals, however, lack alignment, are poorly or ambiguously defined, or are internally inconsistent. This increases uncertainty about what aviation should work towards, how various stakeholders can contribute, and introduces problems with respect to accountability. In order to address this issue, this paper presents a comprehensive definition of a climate neutral air transport system as an “air transport system of which the climate effects of all its greenhouse gases and non-CO₂ effects throughout the entire life cycle of each element of the system is balanced”. The proposed definition spans relevant systems and encompasses all life cycle phases. To achieve a climate neutral air transport system by 2050, all life cycle greenhouse gas emissions and non-CO₂ climate effects remaining after in-sector reduction should be neutralised, as should all remaining non-CO₂ climate forcing from emissions prior to 2050. Clarity on governance is furthermore needed, as the goal and associated targets proposed should be adopted globally.