In this study, hybrid-electric propulsion systems, which have become a focal point in aviation in recent years, were addressed. In order to see the effects of hybrid-electric propulsion systems on fuel consumption, greenhouse gas emissions and flight costs, five different flight times (60, 90, 120, 150, 180 min) and five different cruise altitudes (1200, 1800, 2400, 3000, 3600 m) were compared with conventional flights. The widely used Cessna 172S aircraft was taken as a reference for the conceptual applications in the study. As a result of the study, the hybrid-electric propulsion system achieved the highest fuel and cost savings of 15.1% and 14.2%, respectively, for 120 minutes flight time and 2400 m altitude, while the lowest fuel and cost savings of 9.7% and 9.1% were achieved for 60 minutes flight time and 1200 m cruise altitude. The highest CO2 reduction was 6.86 kg per hour for 120 minutes and 1200 m altitude flight, while the lowest CO2 reduction was 4.47 kg for 180 minutes and 3600 m altitude flight. It has been determined that flights with hybrid-electric configuration have advantages over conventional flights.