Despite aggressive plans to buy new aircraft, China's airlines have been handing them back to manufacturers over the past three years because passenger loads are lighter than expected, according to industry sources. No one is sure how many aircraft have been traded for smaller ones or when the swaps began, but vendors and analysts say they were returned because the Civil Aviation Administration of China agreed to aircraft too big for domestic flights. Guangzhou-based China Southern, for example, operates large Boeing 777s domestically, and Air China flies Boeing 747s between Beijing and Shanghai. 'The buying behaviour of Air China and other companies is lumpy to say the least. It tends to be really very inefficient,' said Stephen Harner, a Shanghai-based analyst with Roland Berger Strategy Consultants. 'Their fleet, I'm sure, is not optimised.' Domestic flights are usually 40 per cent to 50 per cent full, said David Glassman, Shanghai-based partner with the Stern Stewart management consulting company. The industry break-even average is 65 per cent. Stern Stewart ranks China Eastern Airlines, one of the big three in the mainland, as one of the top 10 'wealth destroyers' on the Chinese stock market. 'The load factors are quite low, not as high as they can be,' agreed Wendy Wong, a Hong Kong-based airline industry analyst with Merrill Lynch. 'Usually, [bigger planes] are not used for short hauls unless there's a high load factor.' Chinese purchasing officials said they did not know about trade-ins or could not discuss the subject. However, people in China's aviation industry say they recall such trades. Last year, China swapped two 400-passenger Boeing 747s for 737s because the smaller planes suited capacity, said a manager at Rolls-Royce, which makes aircraft engines. One regional head of an aircraft manufacturer said China had traded back other planes over the past three years, including a number of McDonnell Douglas MD-82's and Russian-made Tupolev aircraft. Some trades were done to modernise fleets rather than to change aircraft sizes. Last year China Southern and Xiamen Airlines ordered 10 Boeing 737s, and news reports in August said Airbus Industrie would sell at least 30 mid-sized planes to China. This week, Airbus added a 185-seat A321 to China Northern's international routes. However, the People's Daily said much of the market until 2019 would go to smaller planes, including 400 made-in-China aircraft for regional flights, which it said would have about a quarter of the market by then. Boeing, which signed a US$2 billion order on October 2 for 30 737s - down from an initial order for 36 - declined to say whether any of its recent deals in China were trade-ins. 'That is their business,' said Hong Kong-based Boeing spokesman Mark Hooper. Zhao Yuna, a spokeswoman for China Aviation Import & Export, which buys Boeings for China, said she knew of no recent aircraft exchanges. However, she said Air China and Shanghai Air still bought larger aircraft.