The smog has become so bad on the mainland that all commercial pilots flying between Beijing and the country's busiest airports must be prepared to land blind. Starting on January 1, the Civil Aviation Administration of China (CAAC) will require pilots of even small commercial aircraft to be certified for instrument-guided landings when travelling between Beijing and other big cities, such as Guangzhou, Shanghai and Shenzhen, the Oriental Morning Post reported yesterday. Currently only those who fly large passenger aircraft, such as an Airbus 330 or the Boeing 767, are required to have such a "blind landing category 2" certification. The report did not specify the size of the aircraft affected by the order, which was issued earlier this year. The order requires pilots to be capable of making instrument-guided landings when visibility falls below 400 metres and when they lack clear sight of the runway. "Smog has become frequent in the country and blind landings will increasingly be used," an unidentified CAAC official told the newspaper. The move is aimed at easing delays at Beijing Capital International Airport, which had the worst flight delays out of 35 major international airports, according to a survey released by FlightStats in July. The official said the mainland pilots' lack of blind landing certification was one reason foreign airlines suffered fewer delays than domestic ones, even when they were landing at the same airports. Their pilots are able to land during poor visibility. About 80 per cent of pilots at Spring Airlines, half of those at China Eastern Airlines and most of those at Juneyao Airlines have already completed the training, the report said. But blind landings require airports keep runways clear of signals that could interfere with the instrument landing system - a radio transmitter that provides a direction for approaching aircraft. Currently, only a few airports on the mainland, such as those in Beijing, Shanghai, Guangzhou and Xian are equipped with the system, although the CAAC has drafted a plan to install them at 26 airports on the mainland. The latest round of smog led to the cancellation or delay of hundreds of flights, stranding passengers and creating chaos at airports. Three passengers on a flight from Nanjing to Nanning were detained after arrival on Monday, as they refused to get off the plane, demanding compensation for a two-hour delay, China News Service reported.