Hanoi, April 23 -- Vietjet has been ranked the lowest-emission airline on intra-Southeast Asian routes, according to the Flight Emissions Review 2025 released by global aviation data and analytics firm Cirium. The report shows that Vietjet recorded emissions of 64.5 grams of CO₂ per Available Seat Kilometre (ASK), outperforming regional peers such as Singapore Airlines (66.7 grams) and Lion Air (67.1 grams). The ranking focuses exclusively on flights operating within Southeast Asia, where short- and medium-haul routes pose greater challenges for fuel optimisation. Cirium's assessment is based on its EmeraldSky methodology, which uses CO₂/ASK as a key metric for carbon emissions per seat offered per kilometre flown, an industry...