A manufacturing defect - not human error - was the cause of the collapse of an air bridge in Chek Lap Kok airport in April, an investigation task force has found.
On April 7, a rear air bridge leading to the entrance of a Cathay Pacific jet bound for Nagoya fell on its side after all passengers had boarded the plane.
As the rear bridge toppled, it dragged the front bridge down with it. An airport worker was injured in the accident.
The task force looking into the incident identified faulty components in a column that supported the collapsed air bridge.
There was a joint comprising two round discs held together by bolts to allow the bridge to move.
The discs' surface should have been even, and they should have fitted perfectly, but a manufacturing defect caused the discs to be convex and uneven, said the task force chairman, independent engineer Edmund Leung Kwong-ho.
As a result, the weight of the bridge rested on the bolts instead of the discs, causing the bolts to wear and break abnormally.
Of a total of 12 bolts, two broke before the collapse and two others showed signs of "metal fatigue". The problem was not discovered during maintenance as the bolts were fixed components and should not be touched in daily operations, Leung said.
As a technician moved the bridge over a hump on the pavement on April 7, the sudden jerk broke the two fatigued bolts, forcing the two discs to split.
Without the pillar's support, the rear bridge then fell on its side and hit the front bridge, causing it to fall as well.
Leung said the hump on the pavement was normal and expected, and the technician had followed procedures when driving over it.
Although it was not necessary to check the joint during regular maintenance, engineers should have inspected the column when they received it from Indonesian manufacturer Bukaka some 15 years ago. The report did not look into procedures carried out during the initial check.
It did not conclude whether anyone was to be blamed for missing the manufacturing defect, or if Bukaka was responsible for the fault.
The Airport Authority's executive director of airport operations, Ng Chi-kee, said the authority would act after looking into a final report to be submitted by the task force.
Meanwhile, the authority has finished inspecting nine air bridges of the same design as the one that collapsed. They have been suspended from use since April. Small gaps were found in the rims of four bridges, which will be repaired or replaced.
The authority also heeded the task force's recommendation to conduct ultrasonic inspections on the bolts every six months.