Here's what you need to know about the LRT bearing problem

Shortly after 5 p.m. on Monday, Ottawa's general manager of transit services issued a terse memo to city councillors telling them what many afternoon commuters had by then already discovered: the entire light rail system was once again out of commission.

"This email is to notify you that, in an abundance of caution, Transit Services is immediately launching R1 [bus] service across Line 1, after a routine inspection revealed an issue with a bearing," Renée Amilcar wrote.

In a second memo later that evening, Amilcar elaborated that during a routine 50,000-kilometre inspection of one of the light rail vehicles, "it was determined that the bearing play was over the threshold at which it could stay in operation."

As a result, all light rail vehicles would be returned to OC Transpo's maintenance and storage facility at Belfast Yard where "every single axle" will be "inspected and checked for any play within the axle hub."

If some of those terms sound familiar, it's because the parts they describe have been central to the problems plaguing Ottawa's light rail system since a train derailed nearly two years ago.

On the evening of Aug. 8, 2021, an eastbound train travelling about 30 km/h derailed about 90 metres east of Tunney's Pasture station.

The train, which consisted of two Citadis Spirit light rail vehicles by French manufacturer Alstom, was on its way to OC Transpo's maintenance and storage facility at Belfast Yard and had no passengers aboard. Earlier that day, it had been removed from service after the operator detected a burning smell.

According to a rail safety advisory letter issued by the Transportation Safety Board (TSB) the following month, one of the train's splined (ridged) axles had likely failed hours earlier while the train was still in service.

When crews attempted to re-rail the train that night, they discovered that one of its wheels was no longer attached to its axle "due to a previously undetected catastrophic roller bearing failure and subsequent axle journal burn-off."

To understand that, it's important to picture how these trains are built. Each two-vehicle train has 10 "bogies," five per vehicle. A bogie is the undercarriage assembly that holds the train's wheels — think of the trucks on a skateboard — three of which are motorized while the remaining two are "trailers."

Each bogie has two axle assemblies, and each axle has two wheels. Each wheel is attached to the axle with a cartridge assembly that holds the roller bearings, and the whole thing is held together with a large locking nut.

After the August 2021 derailment, investigators found roller bearings on the track near uOttawa station, suggesting the failure had occurred earlier that afternoon while the train was travelling west.

Alstom's own investigation determined the failure was due to the undetected loosening of the locking nut that holds the cartridge assembly together.

Within hours of the derailment, the city decided to park its entire fleet of LRT vehicles to inspect each and every axle for loose cartridge assemblies, replacing any showing more than one-tenth of a millimetre of "play." It took five days.

In addition to the cartridge assembly that failed and caused the derailment, the inspections found 17 loose assemblies on nine different vehicles.

According to the TSB, the city has since implemented a "labour-intensive" schedule requiring similar inspections every 7,500 kilometres. The assembly that failed in August 2021 had accumulated nearly 150,000 kilometres before the incident. According to the TSB, it should last for more than 1.2 million kilometres.

The TSB further noted that the construction of these particular cartridge assemblies prevents easy visual inspection for signs of overheating, nor does Ottawa have any wayside or on-board temperature monitoring system in place.

"Consequently, an overheated roller bearing within the cartridge assembly can potentially fail catastrophically without being observed or detected. As demonstrated in this occurrence, such a failure can also lead to derailment if there is no intervention," the TSB wrote in its September 2021 advisory letter.

Despite these warnings, a second derailment occurred within weeks of the first, and the cause was likely related.

On Sept. 19, 2021, a westbound train with 12 passengers aboard derailed near Tremblay station. There were no injuries. Following that derailment, the entire fleet was parked for nearly two months, with service resuming Nov. 12.

The cause of that derailment was loosely, though undeniably, related to the earlier one: An Alstom employee had failed to properly tighten some bolts after replacing a cartridge bearing assembly, part of the remedial work ordered after the August 2021 incident.

In February, the TSB issued another advisory letter expressing concern over "ongoing failures" of the roller bearing assemblies, and noted the city had not acted on its recommendations to monitor the machinery for overheating.

"To date, other than ongoing cartridge assembly free play monitoring, no concrete steps have been taken to resolve the safety deficiency identified in the [previous advisory letter]," the TSB wrote.

In July 2022, a train operator detected an unusual vibration aboard one of the vehicles. Upon inspection, it was discovered that one of the axle hubs was so severely damaged that "catastrophic failure was likely to occur had it remained in service."

The TSB subsequently inspected three cartridge assemblies at its engineering laboratory and discovered widespread damage "not limited to any particular component." Rather, the TSB pointed to the design of the vehicles themselves — Ottawa was the first city to use the Citadis Spirit — and their "more powerful drivetrain."

While other Alstom models use the same cartridge assemblies, the TSB noted Ottawa's articulated trains are longer, heavier and required to carry more passengers at higher speeds than are trains in other cities such as Paris and Istanbul, where there have been far fewer defects.

In addition, the Ottawa Light Rail Transit Public Inquiry noted in its final report in December that the LRT system's "wheel/rail interface" — essentially, how the trains' wheels fit the track — continues to pose a critical concern.

Now a new round of inspections is underway, but there is growing evidence that Ottawa's LRT system could require a dramatic overhaul if it's ever going to provide safe, reliable service to the residents who rely on it.

Writer and editor

After spending more than a decade covering Ottawa city hall for CBC, Alistair Steele is now a feature writer and digital copy editor at cbc.ca/ottawa.