Protruding screws possible cause LRT wheel cracks, TSB says

The Transportation Safety Board (TSB) of Canada says protruding screws may have contributed to cracks found in the steel wheels of Ottawa's new light rail trains. 

The first crack was found July 2, prompting OC Transpo to launch mandatory daily inspections that reduced the number of available trains on the Confederation Line.

Within about a week, four cracks had been found and the TSB announced it would be investigating.

That investigation is ongoing, but on Tuesday the board released an interim advisory letter about a potential cause — one mentioned by the city in September.

The TSB said "jacking" screws, which are used to separate parts of the wheel during maintenance, were already installed when the wheels were shipped.

Normally there's a plastic plug or silicone placeholder in each of the three threaded holes on each wheel, and the jacking screws are inserted later.

"It appears that the change in process was implemented with no requirement for the wheel manufacturer (Lucchini), the LRV builder (Alstom), or the personnel installing the wheels on the bogies to examine the rear surface of the wheel hub to ensure that none of the jacking screws protruded or otherwise interfered with the mating surface of the axle hub," the TSB wrote.

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The board says both it and train maker Alstom have found eight cracked wheels and 116 wheels, or more than 60 per cent of the all the wheels in the fleet, with at least one jacking screw protruding.

While noting its investigation is ongoing and other factors likely led to the cracks, the TSB said all wheels that were shipped with the jacking screws installed should be removed from the trains.

"The preliminary TSB examination results demonstrate that some wheel hub cracks may go undetected and the development of cracks in the area of jacking screws installed in the hub of resilient wheels may be more widespread than initially thought," it wrote.

"Therefore, it is suggested that OLRT and Alstom expedite the removal of all Lucchini resilient wheels that were originally installed on the OLRT LRV fleet and were equipped with jacking screws."

In September, Ottawa's transit operations director Troy Charter said all original wheels would be replaced by spring 2021. In a memo Tuesday, the city said this had happened for 13 of its 38 vehicles.

These safety advisories are issued when the board finds a low- to medium-risk problem, the TSB said. Investigations of this kind usually take about a year.

Ottawa's transportation committee has been getting regular updates on the investigation and is scheduled to meet Wednesday morning.