TAIWAN yesterday detained a hijacker and sent his family back to China after a mainland passenger jet was commandeered and forced to land in Taipei. The low-key approach to the year's first hijacking indicates that authorities will continue Taipei's practice of retaining hijackers for prosecution in the island state's courts. Masquerading as a policeman, Lin Wenqiang, 35, hijacked a China Southwestern Airlines Boeing 737 over Fujian yesterday morning. The hijacking was the 11th pirating of a Chinese passenger jet to Taiwan since early April last year. China and Taiwan officials are yet to agree on how to combat the hijackings. Yesterday, the Taiwan Government information office had by late afternoon still not issued an official statement on the latest incident. Vice-chairman of the official Mainland Affairs Council, Kao Koong-lien, said that Taipei did not encourage hijackings and he called on Beijing to rapidly sign an agreement with Taipei. He accused Chinese authorities of taking a lax attitude towards the issue. The deputy secretary-general for Taiwan's semi-official Straits Exchange Foundation, Shih Ching-ping, said the present policy would continue. Mr Shih said: ''In the absence of an agreement, we will continue to handle this incident in line with the principle of 'separating the hijacker from the aircraft'.'' The plane hijacked yesterday carried eight crew and 122 passengers and was en route from Chengdu to Fuzhou, with a scheduled stop in Changsha. Lin brandished a fruit knife and a fake explosive device made from a teacup and tissues. He demanded to be taken to see the pilot and reportedly threatened to destroy the plane if it was not diverted to Taiwan. Lin allegedly held a knife to the throat of pilot Zhang Hongyun. Mr Zhang asked Lin not to harm any of the passengers or crew. The Taiwanese air force was alerted to the hijack at 10.05 am and two jets intercepted the airline in Taiwanese airspace five minutes later. The plane was escorted to Taipei's international airport and landed at 10.42 am. Airport police took Lin, who was dressed in the uniform of a colonel of the People's Armed Police, and four of his relatives off the aircraft for interrogation. Lin was accompanied by his mother Li Yuying, 68, wife Huang Chunlian, 32, and sons, Lin Changyao, 11 and Lin Changhao, nine. He was apparently seeking asylum for his family. Lin, who comes from Minqing county in Fujian, was a sales manager for the Xinghuo Electrical Equipment Company in Changsha. Taiwan state radio reported that Lin told police he was dissatisfied with corruption in the Chinese legal system and sought freedom in Taiwan. Lin said he conceived the plan for the hijacking after his application to establish a factory had been rejected by authorities in Changsha. However, his family was sent back to China on the hijacked plane when it took off at 2.44 pm. Vice-Justice Minister Lin Shyi-hwu said the relatives had not been involved in the incident and therefore received the same treatment as other passengers. He said the forced return would help curb air piracy. In two previous cases, relatives of hijackers were allowed to remain in Taiwan because they were found to be involved in the hijackings, he said. Unresolved matters related to the hijackings are to be further discussed by the Mainland Affairs Council and the Straits Exchange Foundation at a meeting scheduled for next month. China's Vice-Justice Minister Chiang Hao said after the two bodies met in Beijing last month and reached a ''broad consensus'' that a solution to the problem should be found. ''This is a blow to the relations between Taiwan and the mainland . . . this kind of thing cannot be tolerated,'' he said.