A MARRIED couple hijacked a mainland flight to Taiwan yesterday by threatening to detonate what they said was a bomb - just one day after China vowed to improve air safety to end a plague of crashes and hijackings. The Fujian Airlines Yun-7 aircraft was hijacked while en route from Ganzhou, in the central province of Jiangxi, to Xiamen in coastal Fujian province, where authorities claimed to have tightened airport security early this month. The twin-engined propeller-driven aircraft carried eight crew and 42 passengers, including hijackers Luo Changhua, 38, and his wife Wang Yuying, 34. They took their 12-year-old son with them. The flight took off from Ganzhou at 12.10 pm and was commandeered at 1.10 pm, shortly before it was scheduled to land at Xiamen. Luo allegedly grabbed a crew member and brandished what he said was a bomb. His wife handed a stewardess a message telling the pilot to ''go to Taiwan or the plane will be blown up''. The pilot, Shen Shangming, told the couple the short-range aircraft lacked enough fuel to fly to Taiwan and said he wanted to land in Xiamen. Luo refused. After consulting airport officials in Xiamen, the pilot diverted the plane to Taiwan. Taiwan police later found the bomb to be fake. The couple had put three dry batteries into a vitamin bottle and attached a matchbox with wires to it. Xiamen airport was closed during the flight. A Boeing 747, scheduled to land at 2.11 pm, was thus forced to circle the airport for more than 30 minutes. The hijacking was the third this month and the 10th since April. Most of the other hijackings have involved dummy weapons. One man said he would throw acid over the passengers, but the shampoo bottle he carried had no acid in it. Another ''bomb'' turned out to be a block of soap wrapped in a newspaper with a piece of string sticking out like a fuse. Several hijackers have wielded toy guns. The only real weapons have been knives - even a scalpel, in one recent case. Xinhua (the New China News Agency) carried a brief report on yesterday's incident, but did not say what action airport authorities have taken to tighten security. A senior aviation official told top legislators in Beijing on Monday the national carrier would spend millions more yuan on improving facilities and manpower training to upgrade air safety and service. Legislator Li Yining, an economist, said security checks on passengers before boarding should be stepped up. He also suggested passengers be compensated for the flight delay. Legislators blamed poor management for accidents and substandard service, but did not touch specifically on the hijackings. Taiwan reports said the Luo couple was from Guangzhou, with a brother in Taipei. Authorities allowed Luo's brother to take their 12-year-old son, Wanghuan, to his Taipei home. Luo Changhua was a sales manager in the Nanfang Trading Company and Wang worked as a caretaker. They were interrogated by Taoyuan security personnel and held in custody. The plane was later refuelled and allowed to fly back to the mainland via Hong Kong airspace. Luo told airport police that ''the Communist Party [of China] doesn't respect law''. He said his house had been forcibly torn down four months ago. Angry at theaction, the couple decided to seek asylum in Taiwan. Yesterday's hijacking was the first since five fruitless days of talks over air piracy between the mainland's Association for Relations Across the Taiwan Strait and the Taipei-based Straits Exchange Foundation. In the absence of an agreement, Taipei officials said the current practice of handling hijackers would not be changed. Wu Po-hsiung, Minister for Interior and convenor of a special emergency committee to deal with hijacking incidents, said: ''It is impossible for us to change our policy of separating the hijacker and the aircraft.''