The Housing Department inspected about 1,000 three-bedroom flats in a Tseung Kwan O home ownership estate early this month after a large concrete slab for holding an air conditioner fell two floors from one of the units. It said it would also inspect all similar three-bedroom subsidised flats built by the China State Construction Engineering Corporation in 1997 and 1998 to ensure no similar accident could happen. The department's chief structural engineer, Chan Siu-tack, said yesterday the accident was unusual and that officials were examining records to see how many units fell into the risk category and needed inspection. The inspection was triggered by the accident at Kwong Ying House, Kwong Ming Court, on October 26. No one was injured. So far the department has inspected all slabs in the Kwong Ming Court estate. Three units have been repaired after inspection. Eleven other units were found with cracks in their slabs. Mr Chan estimated repair work would be completed by the end of the month. The seven-year-old home ownership estate has 4,000 units. 'The rusting happened too quickly. It is abnormal. After careful inspection, we believe it was a problem of craftsmanship rather than cost-cutting. Residents shouldn't worry about the safety of the estate. We believe the accident is an individual case,' he said.