Aircraft noise is one of the most significant environmental concerns around airports, generating both social conflicts and financial consequences. This study examined how the fleet composition influences daily exposure to aircraft noise in the vicinity of Poznań-Ławica Airport, focusing on two widely operated aircraft types: the Boeing 737-800 and the newer 737 MAX 8. Measurements were carried out at six monitoring points during 78 operations, and the analysis was based on the sound exposure level expressed on the physical scale and in decibels. The results show that the 737-800 consistently produces higher noise levels than the MAX 8, with mean LASel values of 0.89 Pa²·s (94.5 dB) compared to 0.57 Pa²·s (92.6 dB), a difference of 56%. The gap is particularly evident during take-off, where the 737-800 exceeds the MAX 8 by 137% (2.7 dB). Regression analysis confirmed a decreasing trend in SEL with increasing altitude; in the revised analysis, this dependence is modeled using a log-distance function in dB units, with altitude treated as a proxy for source–receiver distance. The simulation of nine fleet composition scenarios for a representative month showed that increasing the share of MAX 8 aircraft substantially reduces the number of days when the daily equivalent sound level (LAeqD) exceeds the legal threshold of 60 dB. Economic analysis using official Polish penalty tariffs for 2025 also showed that monthly environmental fines could be reduced by up to 69% if the fleet were fully modernised to MAX 8. Even partial renewal, with a 60–70% share of MAX 8, reduced costs by 60–70% relative to a fleet dominated by the 737-800. These findings highlight that fleet modernisation is a highly effective strategy for reducing community exposure to aircraft noise and mitigating the financial burden on airports, although the analysis was limited to daytime operations and one seasonal period.