9 October 2004
Investigation results of the Light Rail broken wheel incident
The Chairman of the Kowloon-Canton Railway Corporation (KCRC) Mr Michael Tien said the Corporation was very concerned about the Light Rail broken wheel incident which happened on 10 September 2004. The KCRC has completed a detailed investigation into the incident and has submitted a report to the Hong Kong Railway Inspectorate of the Environment, Transport and Works Bureau.
On the night of the incident, the KCRC inspected all Light Rail vehicle steel wheel tyres. The Corporation also carried out an ultrasonic flaw inspection of all wheel tyres within a week and no cracks were detected. The existing Light Rail fleet is safe.
Mr Tien reiterated, "The KCRC’s first and foremost priority is to ensure passenger safety. Over the years, the Corporation has undertaken a range of measures to enhance the safety level of our railway systems. The probe into the incident covered a number of areas including the supplier’s production process for the wheel tyre, the Corporation’s procedure on receipt and collection of the products, the maintenance procedure, accountability, and the measures to prevent recurrence of similar incidents."
According to Mr Tien, the KCRC’s contract with the supplier requires that the latter employ an independent and qualified quality inspector to ensure all wheel tyres meet the production standards. The supplier is required to cut open samples of the wheel tyres to test the material and mechanical properties, and conduct ultrasonic flaw inspections on all tyres to ensure they do not have any cracks. This testing and acceptance regime is in line with the British Standard 5892 which is in compliance with international practice. Upon completion of the above procedures, the supplier will issue certificates for all wheel tyres prior to the delivery.
In keeping with its usual practice, the Corporation, upon receipt of the wheel tyres, would conduct ultrasonic inspection on 5% of the batch to further assure the quality of the wheel tyres.
Mr Tien added that the incident was very rare as past record showed that cracks would not develop in new wheel tyres. Investigation conducted by an independent laboratory showed that the processing factory of the supplier had carried out welding repairs to the tyre to cover up defects which appeared in the machining process. After the Light Rail vehicle had been in operation for a certain period of time, cracks appeared inside the welded tyre and grew larger as the mileage built up. The tyre finally fractured when the crack had grown to an extent that it was no longer able to withstand the loading.
Mr Tien said rectification by welding was absolutely forbidden in the manufacturing process. The welding could not be detected by ultrasonic flaw inspection unless the tyre was cut up for examination. However, it was impossible to cut all tyres for examination in the collection process.
While the KCRC was conducting investigation into the incident, the supplier also carried out a detailed examination. It confirmed the investigation results of the Corporation and admitted that there were a total of six wheel tyres in the batch that were welded for rectification, including the one that was broken in the incident. Subsequently, the KCRC has also replaced the other five.
Mr Tien said, "The supplier has admitted responsibility for the violation of procedure. The KCRC will seek compensation for damages from it and will stop awarding it new contracts. I am highly concerned about the incident and will not tolerate recurrence."
Although the KCRC’s existing testing and acceptance and maintenance procedures are in line with international standards, the Corporation will strengthen the procedures to ensure all Light Rail wheel tyres are always in good condition. Details are as follows:

Original procedures:

(1) Routine inspection once every 3 weeks

(2) Ultrasonic inspection in the 24th month of operation

(3) Ultrasonic inspection in the 40th month of operation

Additional measures:

(4) Ultrasonic inspection before installation of all new wheel tyres

(5) Hammering test once every week

(6) Ultrasonic inspection once every six weeks

Mr Tien said that the KCRC would accelerate the existing wheel replacement programme in phases to enhance public confidence in the Light Rail safety. All wheel tyres are expected to be replaced by the end of 2005.
KCRC has also commissioned a group of professionals and academics led by former President of The Hong Kong Institution of Engineers Mr Edmund Leung to review the results of the investigation and to provide independent professional advice. The new measures have already incorporated their views and they all consider the additional measures sufficient for early detection of cracks in wheel tyres, and to prevent recurrence of similar incident. The Corporation will review the measures in six months.