Chinese airlines will enjoy 7.6% passenger traffic growth and buy 4,330 aircraft over the coming 20 years, Boeing says in a forecast that assumes infrastructure constraints and only modest liberalization.

Uncertainties include the extent of competition from fast rail, which the company’s vice president for marketing, Randy Tinseth, says can only become certain over time.

The traffic growth forecast for China compares with a global average of 5.3% over the same two decades. It implies that Chinese airlines will generate 4.3 times as many revenue-passenger kilometers in 2029 as they did last year, but Boeing sees their fleets growing by a factor of only 3.3, partly because aircraft will be used more efficiently.

Tinseth notes that Chinese airlines’ average load factor is less than 75%, compared with about 85% in the United States lately. That, and an assumption that airliners will spend less time on the ground, suggests that Chinese airlines could generate more traffic from each aircraft in the future.

Among the 4,330 aircraft that Boeing expects Chinese airlines to buy, 100 will be new freighters. A further 230 converted freighters, mostly narrow-body aircraft, will be added to the fleet, too, it says.

Chinese growth will be loaded towards the front of the 20 year period, Boeing’s forecast assumes. Tinseth says fleet numbers will double in the first decade—implying fleet growth of about 7.2% a year in that period and then about 5.1% a year in the second decade.

The traffic growth forecasts is barely higher than Boeing’s forecast for Chinese economic growth in the coming 20 years, 7.3%, defying the usual assumption that air travel grows significantly faster than gross domestic product in developing countries. But Tinseth says the relationship breaks down at higher rates of expansion, because of the challenge of supplying infrastructure and personnel, though he notes that China plans to build 97 airports by 2020.

The company has upgraded its outlook for Chinese airlines’ share of international business. And a review of the popularity of sales of single-aisle airline worldwide over the past 10 years has also supported the forecast for unit aircraft sales in China.

Government control over the industry is holding back growth, particularly by favoring the three big carriers owned by the central government—China Southern, Air China and China Eastern. Assuming people and infrastructure were available, the industry could grow much faster if budget airlines were allowed to bloom, but the government shows little sign of dropping its habit of nurturing the big three.

“There is going to be some liberalization in the [Chinese] market,” says Tinseth, playing down the immediate prospects and adding that it would be modest. In China “we don’t have the same type of deregulated market that we have in the United States, Europe or Australia.”

The opportunity for low cost carriers to emerge would come later in the forecast period, he says.

The forecast for 7.6% annual passenger traffic growth is lower than the 7.8% figure that Boeing issued last year, but the difference is partly because the base year has moved from 2008—a bad year, from which a rebound could be expected—to 2009. The front-loading of growth also means that the 20-year forecast growth rate will tend to decline from year to year.