The importance of airport emission inventory is more specific in the local context as it directly affects the local air quality. The specific gap addressed by this research is evaluating the CO2 emission from aircrafts within the landing and take-off (LTO) cycle. Using currently available methodologies for assessing emission within the LTO cycle in the Sri Lankan context has significant limitations, such as unavailability of relevant operational data and the International Civil Aviation Organization (ICAO)-specified “time-in-mode”(TIM) (e.g., take-off, climb-out, idle, and approach) estimates at different phases of the LTO cycle being inconsistent with local conditions. Such industry-wide standards have been found to over or underestimate actual volumes specific to local conditions. In this research, data collected from online flight-tracking services and daily aircraft movement record (DAMR) data maintained by the local air traffic service provider were used to estimate TIM values according to site-specific conditions. Existing literature to some extent addresses the assessment of CO2 emission levels under different phases of flight separately. In this research, a methodology was developed with available data sources to estimate CO2 emission levels under different phases of flight separately within the LTO cycle. The methodology was applied to Bandaranaike International Airport, Sri Lanka. This approach can be applied to similar scenarios in which operational data limitations exist as elaborated in the study.