The country’s largest flight booking website by tickets sold says it will invest 3 billion yuan in a major domestic airline, a move that comes as carriers try to increase direct sales. Caixin reported Ctrip signed the deal with China Eastern Airlines Corp. Ltd., the second largest carrier by passenger numbers, on April 21 in Shanghai. The agreement will see Ctrip buy shares in the airline’s upcoming private placement and increase its stake to 10 percent within a year. That would make the travel website firm the carrier’s biggest outside stakeholder. The firms said they will also collaborate on a range of projects, including developing budget airlines and travel insurance products.