Inadequate monitoring of the troubled Ngong Ping 360 cable car meant engineers missed two chances to spot problems which led to a system failure that left 800 passengers stranded in mid-air, an investigation report has revealed. The Lantau attraction has been closed since the incident on January 25, when vibrations triggered a sensor on the bullwheel, which winds cable, bringing the system to a halt. Service should resume tomorrow after an inspection by the Electrical and Mechanical Services Department. The attraction's managing director, Wilson Shao Shing-ming, said the cable car, which has suffered a string of technical problems since opening in 2006, was now 'more reliable' - but he stopped short of promising there would be no more shutdowns. According to the department's report, released yesterday, monitoring engineers first noted rising vibration in bullwheel bearings on December 16. But they decided it was not serious enough to halt operations. Wear and tear on the bearings and the lining of the bullwheel, possibly caused by inadequate lubrication, led to more vibration. Two days before the breakdown, a routine measurement of the lining of the bullwheel found that 'three out of a total of 12 measurement points marginally exceeded the wear limit'. Engineers had planned to replace the lining within two weeks, in accordance with guidelines. 'The current interval of vibration monitoring is not able to ensure early identification of defects on the bearings and their timely replacement,' the report said. The failure at Lunar New Year, which occurred as temperatures plunged to 3 degrees Celsius, was the fourth technical fault in two months. Professor Lo Kwok-keung, of Polytechnic University's department of mechanical engineering, said the bearings should have been repaired after the December test. 'If they had been, the passengers wouldn't have been stranded,' he said. The operator has improved vibration monitoring and will 'capture data on an ongoing basis', which will be studied every two weeks, the report said. It previously analysed vibrations only every four months. It will also improve handling of the lubricant it uses, as excess water in the lubricant was one possible cause of the wear and tear. Engineers have previously blamed heavy usage for the problems that have dogged the system. After an empty cable car plunged to the ground in 2007, experts said the system should be in operation for no more than 250 hours per month to allow time for maintenance.