American Airlines (AA, Dallas/Fort Worth) has purchased 9.7 million shares, representing a 20.8% stake, in Republic Airways Holdings, the holding company of Republic Airways and Mesa Airlines, it announced in a filing to the US Securities and Exchange Commission (SEC).

Following the investment, American joins ‘Big Three’ rivals United Airlines and Delta Air Lines in holding an investment in Republic, which after its merger with Mesa, became the largest regional carrier in the United States, with about 300 Embraer E170 and E175 aircraft.

Moreover, American Airlines now has the largest investment in Republic, with United holding about 7.7 million shares and Delta around 6.7 million shares, or stakes of 18.2% and 14.4%, in the company.