Assessment of Carbon Dioxide Emission Metric Systems for an Aircraft Certification Standard

To mitigate aviation CO2 emissions, the International Civil Aviation Organization's Committee on Aviation Environmental Protection is considering an aircraft CO2 emissions certification requirement. This paper presents an evaluation of potential CO2 metric systems for their suitability as a basis for an aircraft CO2 certification requirement. Candidate CO2 metric systems, consisting of a metric, a correlating parameter, evaluation conditions, and a notional limit line are assessed against a set of key criteria. The metric systems were chosen to reflect aircraft fuel consumption, which directly correlates with CO2 emissions for a given fuel type. Key criteria were identified to represent desirable attributes of the metric system, that is the ability to represent fuel efficiency performance improvements, validity across a range of aircraft types, correlation with fuel efficiency in actual operations, fairness across stakeholders, ease of measurement, and robustness against unintended consequences. The analysis showed a metric system consisting of a metric based on the inverse of the specific air range correlated with the maximum takeoff weight evaluated at 85% of maximum takeoff weight reasonably satisfied the key criteria.