Revenue generation has a positive and significant effect on the growth of any business. The existing work process in Nigerian Airspace Management Agency (NAMA) billing system creates the loophole for revenue deficit. The need to enhance the billing system of this organization prompted the need for this study. Primary data were collected from NAMA station at Muritala International Airport and its corporate headquarters. The data include the process and time of attending to airlines or their agents (which includes arrival time, service time, departure time, Waiting time etc.), Six months financial statement of NAMA MMIA, Debt profile details for debtors and number of airlines attended to per day. These data formed the input for developing the SimPy model to bring together process based discrete events. Validation was done by comparing the simulated results with the real results using statistical t-test at p less than 0.05 (p<0.05). 15 airlines were considered for 5 months (assuming 30 days per month), making an average of 6 landings per day per route which represents 3 flights within a route per day. The rate is ₦7,000 per one-hour flight per route. The simulation results reveal that with the proposed model ₦23,948,044 was generated as against ₦12,486,680 of the existing system. This represents 191.788% improvement. This result is for Murhitala Muhammed International Airport (local wing) only. The python simulation package (SimPy) used, introduced approval levels for the various department, thereby ensuring no departments' function was undermined. This model is useful for Airspace management, in that it reduces deficit without any negative impact on the safety and service delivery of airlines.