In late April, Air China and China Eastern Airlines both won approval to launch new flights between Shanghai and London, breaking a longtime unwritten rule that only one Chinese carrier can operate a major intercontinental flight between a particular Chinese city and the United States or Europe.

For years, flights between Beijing and New York have been operated by Air China, in addition to flights operated by US carriers. No other Chinese carriers have been allowed to join the competition.

In principle, international flights from a Chinese city to a city in the US or Europe, except Moscow, should be operated by one Chinese carrier, according to earlier regulations of the Civil Aviation Administration of China.

"Many years ago, when the domestic aviation sector was still in its initial development stage, the authority issued the policy to support the growth of Chinese air-lines," said Lin Zhijie, an aviation industry analyst and columnist at Carnoc, a Chinese civil aviation website.

"Now, the overall strength of Chinese carriers has significantly improved, and their market share in the routes between China and the US, as well as China and Europe, is already higher than foreign carriers," he said.

"Still following such a policy would restrict business competition in the current situation. With no competition between domestic players, during busy seasons, flight ticket prices of those international flights stay high."

To solve the problems, last year, CAAC released new management measures for flight resource allocation and the use of international flight rights. When certain requirements are met, airlines don't need to be restricted by the old rule of one route being exclusively flown by a single Chinese airline, according to the new regulations.

For instance, for routes on which Chinese and foreign carriers both have operations and the market share of Chinese carriers is less than 70 percent, and when the weekly total capacity is more than 14 flights, Chinese airlines don't need to follow the single-domestic-airline rule.

In addition, on routes that have been only flown by Chinese carriers for more than six years, and on routes that have been flown for more than three years and no new Chinese carriers have become new operators in the past three years, the old rule no longer applies.

The route connecting Shanghai and London became the first international flights that are operated by multiple Chinese airlines after the issuance of new regulations. CAAC will score applicants based on 16 indexes, including consumer benefits, the development of hub airports, efficiency of the use of flying rights and operation safety and quality.

Every index has certain methods of calculation, and airlines that score highest will get the flying rights, according to the new regulations.

Previously, Shanghai-based China Eastern was the only operator of the Shanghai-London route. This year, Air China, China Southern Airlines, Shanghai Airlines and Juneyao Air applied to fly the route. China Eastern and Air China, respectively, stood out from intense competition with their higher scores.

"Under the new scoring rules, it would be more difficult for medium and smaller airlines to apply for international flights between second- and third-tier Chinese cities and foreign cities," Lin said.

Meanwhile, a number of other routes, such as flights connecting the soon-opening Beijing Daxing International Airport and Paris, with four carriers applying, are awaiting the results of scoring.