Aircraft refuelling is a major cause of flight delays because it is a slow process. Further, if it does not begin as soon as the aircraft is available for ground handlers, there is an increasing risk of it being terminated after the final passenger has boarded. Usually, the process only begins after information regarding the required quantity of fuel is passed through the flight dispatcher, and this information typically requires a certain time to reach the ground handlers. Therefore, it is intended to test a new scenario: to begin refuelling with a minimum level and, if necessary, fill up the remainder with the final fuel figures when received. The aim of this paper is to analyse the application of Six Sigma in this process through Student’s t-test and statistical process control. The collected data in this case study include the amount of fuel supplied and flight delays (which are mainly caused by refuelling). The results demonstrate that the new process is favourable, and that the average length of flight delays is reduced from 14 to 6 min, which is an improvement of 57%. It is concluded that the application of Six Sigma in the aircraft refuelling process saves time and improves on-time performance levels, which is relevant to the scientific literature, thereby aiding in mitigating the risk of fines and penalties.