This study aims to determine the impact of airline companies’ internal and external financing decisions on fixed asset investments. For this purpose, 25 airline companies worldwide were divided into two groups, with a market value greater than 10 billion dollars (BigCap) and below (SmallCap), and analyzed using the panel data method. External financing sources have a negative effect on fixed asset investments for BigCap airline companies, while external financing sources have a positive effect on SmallCap airline companies. Equity financing, return on assets, and net profit margin have statistically significant positive effects on fixed asset investments in SmallCap companies, while these effects are not statistically significant for BigCap companies.