HONG KONG – China ordered the nation's commercial pilots to learn to "land blind" in smoggy conditions to help ­alleviate chronic flight delays.

Pilots flying to Beijing's international airport from the nation's 10 busiest airports must be qualified to land when visibility falls below 1,300 feet, starting from Jan. 1, the official China Daily said. The new requirement, translated as "level two blind landing," uses radio beam transmitters to guide planes when pilots have difficulty seeing, according to the Xinhua News Agency.

Smog is hurting efforts to improve on-time performance in China, where about one in four flights is delayed because of airspace congestion. Haze that engulfed Shanghai this month sent air pollution to record highs, causing cancellation of more than 200 flights in a 24-hour period.

Beijing and Shanghai had on-time departure rates of 38 percent and 39 percent in October respectively, worst among 35 major international airports, according to Oregon-based FlightStats Inc.

Shanghai-based China Eastern Airlines Corp Ltd., the nation's second-biggest carrier, has 1,400 pilots that are qualified to meet the new requirements, the company said.

Training underway

Spring Airlines Co., China's largest outside government control, said it's training pilots to land in smog.

Hong Kong-based Cathay Pacific Airways Ltd. said the new rule would only apply to mainland Chinese carriers.

In January, Beijing suffered its worst bout of air pollution, with PM2.5 readings hitting at least 886. Shanghai's air pollution index surged to a record 482 on Dec. 6 into the "severe" level, the highest of a six-tier rating system.

The haze also caused traffic congestion in the nation's commercial hub as the government took such emergency steps as ordering cars off the road and factories to cut production.

The average concentration of PM2.5, particulate matter that is smaller than 2.5 microns in diameter, was 76 micrograms per cubic meter in 74 cities in the first six months, according to the environmental protection ministry. That's nearly three times the level of daily exposure recommended by the World Health ­Organization.

Top cause of social unrest

Premier Li Keqiang pledged in March to clean up pollution, including cutting coal consumption, shutting steel plants and controlling the number of cars. Pollution has become the top cause of social unrest in China, according to Chen Jiping, a former leading member of the Communist Party's Committee of Political and Legislative Affairs.