The world's largest airlines can be defined in several ways. American Airlines Group is the largest by its fleet size, revenue, profit, passengers carried and revenue passenger mile. Delta Air Lines is the largest by assets value and market capitalization. Lufthansa Group is the largest by number of employees, FedEx Express by freight tonne-kilometers, Ryanair by number of international passengers carried and Turkish Airlines by number of countries served.
In recognition of the essential national economic role of a healthy aviation system, Congress authorized partial compensation of up to $5 billion in cash subject to review by the U.S. Department of Transportation and up to $10 billion in loan guarantees subject to review by a newly created Air Transportation Stabilization Board (ATSB). The applications to DOT for reimbursements were subjected to rigorous multi-year reviews not only by DOT program personnel but also by the Government Accountability Office[46] and the DOT Inspector General.[47][48]