OTTAWA -- The Rideau Transit Group (RTG), which built and now maintains the Confederation Line LRT system in Ottawa, says a "handful" of light rail vehicles require further inspection following a minor derailment incident last week.

Despite some trains remaining out of service, however, OC Transpo says service on Monday should not be significantly affected.

An empty train that was leaving Tunney's Pasture Station to return to the maintenance facility on Belfast Road was stopped last Sunday night after the operator experienced an unusually rough ride. One of the train's 10 axles had left the tracks. No one was hurt and the train remained upright.

The entire Confederation Line was shut down and service did not resume until Saturday morning. Crews had to use a rail dolly to walk the derailed train from Tunney's Pasture to the maintenance yard Wednesday, a process that took most of the day.

OC Transpo said an investigation revealed that part of the axle bearing assembly was ever so slightly loose, which caused the initial issue.

"This movement caused damage to the bearings inside the unit and wheel, which in turn lead to the axle coming off the track on Sunday evening," Transportation Services General Manager John Manconi said in a memo Friday night, describing the movement of the component as "fractions of a millimetre."

Every train on the line had to be fully inspected before returning to service.

RTG said in a release Sunday morning that many trains have cleared the inspection and safety certification but they found "a handful of vehicles" that require further investigation.

"The total number of vehicles affected will only be known once the inspections are completed. These vehicles will be removed from the revenue service fleet until the component is replaced," said RTG's director of communications Helen Bobat.

Bobat said RTG plans to increase service on the line as the investigation into the problem—and the work to resolve it—continues.

When service resumed at 6 a.m. Saturday, OC Transpo said trains were running every 10 minutes. By Saturday afternoon, the wait time had been reduced to eight minutes. OC Transpo says there is enough capacity on the line to carry all customers without overcrowding.

Trains are now running every five to six minutes, according to OC Transpo, which is typical for Sunday service. In a memo to city council Sunday afternoon, Manconi said he expects trains will run every five minutes on Monday.

"This a similar service level provided over the past several months, and based on recent ridership counts, will provide enough capacity to accommodate weekday customers. We will continue to work with RTM to increase service further, in preparation for the likelihood of increased ridership in September," Manconi wrote.

"OC Transpo continues to have buses on standby at strategic locations across the alignment to assist should customer loads be higher than anticipated."