Scaled-back Metro service with waits as long as 40 minutes will continue until mid-November while transit officials determine how to safely return rail cars suspended after a derailment.

Metro General Manager Paul J. Wiedefeld said Thursday the transit agency is developing an early-detection system for wheels and axles to screen for a progressive defect that has caused some wheels to move outward, putting trains at risk for derailment. After the plan is submitted to an independent commission that oversees Metrorail safety, Wiedefeld said the transit agency will need at least two weeks for testing.

“We are working as hard as we can to get that legacy fleet back out there, but it takes time,” he said, adding that a return is unlikely to occur before at least Nov. 15. Wiedefeld also acknowledged for the first time Thursday that he hadn’t been aware of the defect.

The new timeline was revealed during Metro’s board meeting, which included the most detail Metro has released about contingency plans for operating the rail system and a defect that sidelined its 7000-series trains. Metro’s basic service levels come at a rough moment for a transit agency that hoped for a resurgence among pandemic-weary riders but finds itself amid its largest crisis in six years.

Metro has been relying on about 25 percent of its rail cars since Oct. 17, when the independent Washington Metrorail Safety Commission ordered the agency to pull the 7000-series cars from service. The defect, in which the distance between wheels widens outward on their axles, has been found more than 50 times over four years, with most of the failures surfacing this year.

The problem came to light Oct. 12, when a single car on a Blue Line train slipped off the tracks outside the Arlington Cemetery station, prompting the evacuation of 187 passengers. The National Transportation Safety Board launched an investigation that showed the defects had been uncovered during Metro inspections since at least 2017.

Metro had been in discussions with car manufacturer Kawasaki Rail Car about the defects, but transit officials did not notify the safety commission. Metro is required to report rail car deficiencies to the commission, a government agency that monitors and oversees Metrorail safety.

Metro board members have said they were not told of the defects. In a rare instance of board chairman Paul C. Smedberg holding Metro’s chief executive up to public scrutiny, he asked Wiedefeld if he had known about the defects. Since being appointed chairman following a board ethics scandal in 2019, Smedberg and Metro management have generally spoken with a unified voice on major issues.

“Mr. Wiedefeld, I’ve heard from, I can’t tell you how many stakeholders and interested parties about this incident in the last week or so, and every single one of them says they find it very hard to believe, given your track record and what you’ve done for this organization, that if you knew about this, that you wouldn’t have done something,” Smedberg said. “Did you know?”

“No, I did not,” Wiedefeld said.

Smedberg followed, “Do we have enough information yet to know where the accountability lies for this?”

“I think it’s too soon, “Wiedefeld said. “I think that we let the investigation take its course, and we will deal with those issues. But I think it’s the right thing to do to let the investigation run its course, [and] that will lead us to wherever it leads us.”

Since being hired to lead Metro after a passenger’s death from smoke inhalation on a stalled train in 2015, Wiedefeld has stressed his safety-first commitment, prioritizing a multimillion-dollar SafeTrack maintenance and safety program while curbing late-night rail service to give maintenance workers more time for repairs and inspections.

The NTSB this month said the wheel assembly defect could have led to a catastrophic incident. Investigators described the problem as rare, surfacing after a period of time or miles, and said the defect probably originated either during construction of the rail cars or the assembly of their wheels and axles.

The flaws appeared between two and five times a year between 2017 and 2020 before inspections this year turned up 18 cases. The NTSB found at least 21 more incidents this month during an examination of all 7000-series cars.

Riders and elected officials have called for consequences and accountability at the transit agency for allowing riders to use the 7000-series trains as the defects mounted.

“Just as children were getting back into a school routine and after dealing with 1 ½ years of pandemic, now all the kids that were planning to rely on Metro have to deal with another major interruption,” Jon Samuel, a District resident, wrote in a public comment to Metro’s board that was read during Thursday’s meeting. “Metro had 1 ½ years of low ridership to deal with this, and it is infuriating that poor leadership necessitates dealing with it now.”

Metro officials said they initially viewed the problem as a warranty issue in a handful of cars until this year, when the defect appeared more frequently.

While Metro Chief Safety Officer Theresa M. Impastato could not discuss details Thursday of the NTSB investigation, she walked board members through the transit agency’s inspection process, which first discovered the defects. She said that every 90 days during routine inspections established by manufacturer recommendations, transit workers measure the distance between sets of wheels “to ensure that the wheels have not migrated.”

Rail cars with wheels that have moved outward are pulled from service. Impastato said Metro is working with the safety commission and the NTSB to have defective wheel sets analyzed by an independent company or agency. She said Metro is also working with Kawasaki to complete an analysis of the failures.

The safety commission has allowed Metro to propose a plan that would return non-defective 7000-series cars back to service — without knowing the reason for the malfunction — that assumes frequent inspections or other detection methods. Metro is working with safety commission officials on the plan, which had not been formally submitted Thursday.

After Metro develops the parameters of a wheel-inspection system, Wiedefeld said it must run tests to ensure the process is effective.

The 7000 series is Metro’s latest model of rail car, joining the fleet between 2015 and 2020 at a cost of about $2 million a piece. It makes up 748 cars of the agency’s nearly 1,200-car fleet.

Without them, Metro is running basic service, with trains operating every 15 to 20 minutes on the Red Line and 30 to 40 minutes on other lines. Silver Line trains are operating between the Wiehle-Reston East and Federal Center SW stations.

Also limiting Metro’s ability to run train service is the absence of its 6000-series trains, which started to be phased into service in recent weeks after two train separations last year. As Metro slowly adds those 184 cars, they join older-model train sets from the 1980s, giving Metro 31 trains for the 91-station system.

The transit agency also hopes to cobble together about 20 more trains as it pulls more 2000- and 3000-series cars out of storage.

“To put the 2000-series rail cars back in service, a series of component change-outs need to be performed, followed by a thorough inspection, and [they] are then cleaned,” Metro Chief Operating Officer Joseph Leader said. “It sounds easy, but with limited yard, tracks and shop availability, the overall task will take some time.”

The additional trains are not likely to reduce wait times but will be called on when stations or lines experience crowding.

“Additional trains as they become available will be strategically used to address the most crowded areas and improve reliability of basic service,” Leader said. “Each day, we will continue prioritizing strategic deployment of trains ready to enter service to reduce crowding.”

Busy stretches likely to see additional trains include the Red Line in the direction of the Glenmont station during the afternoon rush and on the Green Line toward Branch Avenue during that same time.

Metro’s train shortage comes as more downtown and federal offices reopen and as new coronavirus infections in the United States have dropped nearly 60 percent since a September spike. Business and civic leaders say a fully functioning Metro system — the nation’s third-largest — is crucial to the D.C. region’s economic recovery.