We studied a methodology for flight trajectory optimization, and also the workloads of air traffic control officers (ATCOs). Case studies were conducted through simulations for flight trajectory optimization. The aircraft model was A320-200s, which is pre-dominantly utilized in Southeast Asia for short to medium range flights. Fuel savings were computed for selected routes, and were compared with that of existing operations and flights simulations, which revealed significant fuel savings. The research also determined the coefficients of ATCOs’ workloads and demonstrated dynamic sectorization in selected airspace of Southeast Asia. It was found that dynamic sectorization was more efficient than static sectorization in balancing the workloads of ATCOs, reducing the standard deviation by 50% and the balance of workloads among sectors by 12.9%.