Human error might be the cause of the latest glitch, the fifth of its kind, on the Wen-Hu line of the Taipei MRT system, city authorities said Thursday. Tan Guo-guang, Taipei City's deputy secretary-general, told a news conference later that day that an investigation had been launched to find the cause of the accident, which he acknowledged may have been the result of human error, although he also said it could have been caused by limited space in the system's maintenance plant and inadequate platform length. Although the incident -- a collision in the morning between two trains that were being recalled for routine maintenance -- did not affect normal passenger services, Tan said some devices and components, including window glass, connectors and switches, were destroyed by the collision. Initial damage was estimated at over NT$1 million (US$30,000) , Tan added. According to Chen Chung-liang, director of the city's Department of Rapid Transit Systems, the two trains collided when approaching a set of points on two separate tracks at the Neihu depot where they were to be checked. The two trains collided because one was being operated manually rather than by the system's computers, Chen explained. He promised a detailed examination of the entire system by experts within two days, but did not say when a report on the incident would be submitted. Meanwhile, a group of Taipei city councilors demanded that the city government and Bombardier -- the system's engineering contractor -- provide a clear explanation of the collision. The councilors, including Chin Lee-fang of the ruling Kuomintang (KMT), as well as Lee Wen-ying, Cho Po-ya and Lee Chien-chang of the opposition Democratic Progressive Party (DPP) , issued the demand after inspecting the repair and maintenance depot in Neihu. Since it began service in March this year, the line has recorded previous major malfunctions March 21, July 1, Aug. 9 and Oct. 16, a frequency of incidents the councillors blasted as totally unacceptable. 