A year and a half after announcing the merger, the FAA's action means that all flights by the two carriers now operate as American Airlines flights. The FAA decision comes only weeks after the two airlines merged their loyalty reward programs under American's AAdvantage program.
The airline has reached five-year collective bargaining agreements with the pilots and flight attendants of the two carriers.
The key outstanding steps needed to complete the integration are the merger of the two reservation systems and the adoption of employee agreements that put all worker groups from the two airlines into the same contracts.
The US Airways planes are being painted with the American colors and logos.
When the integration is completed, most likely by the end of 2015, American Airlines will be the world's largest carrier with more than 110,000 employees and a fleet of nearly 1,000 planes, operating about 6,700 daily flights. The parent company, American Airlines Group, is based in Fort Worth, Texas.